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Cross-Lingual Transfer for Machine Translation in Turkic Languages

Omer Burak Cinar, Mehmet Mert Dalkilic, Cagri Toraman

Year: 2026Venue: arXiv preprintArea: cs.CLType: PreprintEmbeddings: 95

Intelligence

Status: succeeded | Model: Gemma-4-26B-A4B | Prompt: intel-v1 | Confidence: 94%

Last extracted: 8/3/2026, 2:57:03 AM

Summary

This study investigates cross-lingual transfer in machine translation among five Turkic languages (Turkish, Azerbaijani, Uzbek, Kazakh, Kyrgyz) using the mT5 model. The authors construct pairwise transfer matrices to analyze how transfer strength varies based on linguistic relatedness, transfer direction, and the fixed translation target. Key findings include stronger transfer between closely related language pairs (e.g., Turkish-Azerbaijani, Kazakh-Kyrgyz), significant asymmetry in transfer direction, and the impact of script alignment (Latinization) on performance metrics like BLEU and chrF.

Entities (11)

Azerbaijani · language · 99%Kazakh · language · 99%Kyrgyz · language · 99%Turkish · language · 99%Uzbek · language · 99%BLEU · metric · 95%chrF++ · metric · 95%mT5 · model · 95%Turkic Languages · language-family · 95%Cross-lingual transfer · concept · 90%Latinization · process · 85%

Relation Signals (10)

Turkish → belongstofamily → Turkic Languages

confidence 99% · We study transfer among five Turkic languages; Turkish...

Azerbaijani → belongstofamily → Turkic Languages

confidence 99% · We study transfer among five Turkic languages; ... Azerbaijani...

Kazakh → belongstofamily → Turkic Languages

confidence 99% · We study transfer among five Turkic languages; ... Kazakh...

Kyrgyz → belongstofamily → Turkic Languages

confidence 99% · We study transfer among five Turkic languages; ... Kyrgyz

Uzbek → belongstofamily → Turkic Languages

confidence 99% · We study transfer among five Turkic languages; ... Uzbek...

Turkish → strongtransferto → Azerbaijani

confidence 90% · transfer is strongest between closely related Turkic pairs, especially Turkish-Azerbaijani

Kazakh → strongtransferto → Kyrgyz

confidence 90% · transfer is strongest between closely related Turkic pairs, especially ... Kazakh-Kyrgyz

mT5 → usedfor → Cross-lingual transfer

confidence 90% · Across mT5 experiments, we find that transfer is strongest...

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Abstract

Abstract:Cross-lingual transfer is central to low-resource machine translation, but its behavior within closely related language families remains insufficiently characterized. We study transfer among five Turkic languages; Turkish, Azerbaijani, Uzbek, Kazakh, and Kyrgyz; using pairwise transfer matrices. In this setting, each model is fine-tuned with one transfer source and evaluated on a different transfer target while the translation target remains the same. Across mT5 experiments, we find that transfer is strongest between closely related Turkic pairs, especially Turkish-Azerbaijani and Kazakh-Kyrgyz. We also show that transfer direction matters, and that the same transfer source-transfer target pair can behave differently when the translation target changes. Latinization improves BLEU and chrF in several script-mismatched settings, but its effect is not uniform across metrics. Additional analyses show that transfer sources are mostly stable across different datasets and model settings.

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Cross-Lingual Transfer for Machine Translation in Turkic Languages Omer Burak CinarMehmet Mert DalkilicCagri Toraman Middle East Technical UniversityMiddle East Technical UniversityMiddle East Technical University Computer Engineering DepartmentComputer Engineering DepartmentComputer Engineering Department cinar.burak@metu.edu.tr mert.dalkilic@metu.edu.tr ctoraman@metu.edu.tr Abstract Cross-lingual transfer is central to low-resource machine translation, but its behavior within closely related language families remains insufficiently characterized. We study transfer among five Turkic languages—Turkish, Azerbaijani, Uzbek, Kazakh, and Kyrgyz—using pairwise transfer matrices. In this setting, each model is fine-tuned with one transfer source and evaluated on a different transfer target while the translation target remains the same. Across mT5 experiments, we find that transfer is strongest between closely related Turkic pairs, especially Turkish–Azerbaijani and Kazakh–Kyrgyz. We also show that transfer direction matters, and that the same transfer source–transfer target pair can behave differently when the translation target changes. Latinization improves BLEU and chrF in several script-mismatched settings, but its effect is not uniform across metrics. Additional analyses show that transfer sources are mostly stable across different datasets and model settings. 1 Introduction Neural Machine Translation (NMT) [45] has largely replaced earlier statistical and rule-based machine translation systems. Attention mechanisms [5] and the Transformer architecture [52] have substantially improved translation quality, but low-resource settings still remain difficult because high-quality parallel data is scarce [25]. Transfer learning is therefore widely used to share knowledge across languages [59], especially when languages are typologically related and share vocabulary or morphology [21]. The Turkic family is an unusually useful test bed for pairwise transfer. It combines typological relatedness with noticeable asymmetries in resource level and script: Turkish and Azerbaijani are written in Latin script, while Kazakh and Kyrgyz are commonly written in Cyrillic; Uzbek is mixed in practice but often processed in Latin. This combination creates a controlled setting in which transfer can be studied across related languages while still exposing the effects of script alignment and resource imbalance. Much existing evidence in multilingual MT comes from English-centric settings, where English is often used as the main source, target, or pivot language in training and evaluation [14]. When English is used as the fixed target language in evaluation pairs, transfer from one source language to another is observed only under English as the target. This does not show how the choice of target language changes cross-lingual transfer. To study this effect within the Turkic family, we use Turkic languages as target languages and ask a more fine-grained question: for a fixed target language, which source language is the best fine-tuning donor for each unseen evaluation source, and does that preference remain stable when the evaluation source, script representation, dataset, or pretraining regime changes? Although target-aware data selection has been studied in multilingual NMT [54], pairwise transfer between source languages under different Turkic target languages remains less explored. We address this gap by constructing fixed-target transfer matrices among five Turkic languages. Throughout the paper, we distinguish between translation direction and transfer direction. The translation source is the language from which a sentence is translated, and the translation target is the language into which it is translated. For example, in Turkish-to-Azerbaijani translation, Turkish is the translation source and Azerbaijani is the translation target. In our fixed-target transfer setting, we additionally define a transfer source and a transfer target. The transfer source is the source language arXiv:2607.29355v1 [cs.CL] 31 Jul 2026 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. used during fine-tuning, while the transfer target is the source language used only at evaluation time. For instance, if a model is fine-tuned on Turkish→Azerbaijani and evaluated on Uzbek→Azerbaijani, then Turkish is the transfer source, Uzbek is the transfer target, and Azerbaijani remains the fixed translation target. This design measures the contribution of the transfer source to the transfer target under the same translation target. Our study is organized around three research questions: RQ1. Which Turkic languages transfer most effectively to unseen languages in cross-lingual machine translation? RQ2. How does the choice of translation target affect cross-lingual transfer? RQ3. How does transliteration into the Latin alphabet affect Turkic cross-lingual transfer? Our main contributions are as follows: C1. To the best of our knowledge, we present the first MT-based pairwise transfer matrix for five Turkic languages. C2. Unlike prior transfer studies that rely on non-Turkic pivot languages, we use Turkic languages as both translation sources and targets, enabling a controlled analysis of transfer behavior within the same language family. C3. We release our best-performing Turkic machine translation models together with the book-aligned parallel pairs created for this study. 1 2 Related Work Research in multilingual neural machine translation (MNMT) has extensively studied how transfer emerges across languages, when it is beneficial or harmful, and how data composition shapes these dynamics. We summarize the literature along three axes: (i) transfer learning and cross-lingual transfer, (i) multilingual interference and directionality, and (i) machine translation for low-resource and Turkic languages. 2.1 Transfer Learning and Cross-Lingual Transfer Transfer learning plays a central role in low-resource machine translation. Zoph et al.[59]show that transferring parameters from a high-resource parent model to a low-resource child model yields significant improvements. Subsequent work demonstrates that transfer is strengthened by linguistic similarity and shared sub-word vocabularies [33], and that even simple continued training can yield strong gains without architectural changes [22]. Later analyses confirm that transfer is most effective for low-resource and closely related language pairs [21]. Recent work has focused on measuring transfer more explicitly. Representational Transfer Potential (RTP) [43] captures positive and negative transfer via representation similarity rather than surface metrics. Large-scale studies such as ATLAS [28] and Interference Matrix [2] further show that transfer is asymmetric and strongly influenced by language family and script similarity. 2.2 Multilingual Interference and Directionality Although multilingual training enables parameter sharing across languages, adding more languages or mixing imbalanced data does not always improve performance. Prior work has identified capacity 1 https://github.com/TurkicTransfer/Cross-LingualTransferforMachineTranslationinTurkicLanguages 2 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. limitations and negative transfer in multilingual models, often described as the curse of multilinguality [10]. This issue is especially relevant for low-resource language families, where dominant high-resource languages may help some transfer directions while hurting others because of inter-language parameter competition [6, 27]. Directionality is also important for cross-lingual transfer. Prior work on joint multilingual training shows that translation tasks can interact positively, negatively, or asymmetrically, where one task improves while the other degrades [53]. Other studies investigate target-aware data selection in multilingual NMT [54] and the role of translation direction in multilingual training [30]. However, less attention has been given to the direction from transfer source to transfer target, especially how this direction changes under different translation targets. Our work focuses on this setting by constructing pairwise transfer matrices among Turkic languages. 2.3 Low-Resource and Turkic Machine Translation Low-resource machine translation is often constrained by the scarcity of high-quality parallel data. Backtranslation [41] is commonly used to create synthetic parallel data by translating monolingual target-language data into the source language, and high-resource pivot languages such as English are also used to support data construction [20]. Beyond data creation, low-resource MT also depends on methods for finding and assessing useful parallel sentence pairs. Sentence embedding models such as LaBSE are effective for low-resource bitext mining [9], while large language models can support translation quality assessment and filtering decisions [23]. Turkic languages present a particularly challenging low-resource setting because many language pairs have limited direct parallel data, and the family also includes differences in script and resource availability. Prior work has demonstrated the usefulness of Turkish as a high-resource pivot for improving NLU performance across other low-resource Turkic languages [40]. In machine translation, multilingual training for Turkic languages has also been shown to improve performance through joint training [32]. Building on this line of research, we provide a comprehensive cross-lingual analysis of Turkic MT transfer, examining how transfer patterns change across Latinization, model architectures, evaluation datasets, and continual pretraining settings. 3 Data We use three types of data: monolingual corpora for continual pretraining (CPT), bilingual corpora for fine-tuning, and held-out evaluation datasets. The study covers Turkish (tr), Azerbaijani (az), Uzbek (uz), Kazakh (k), and Kyrgyz (ky), denoted by their respective ISO 639-1 language codes. For CPT, we collect monolingual data from publicly available sources, including Wikipedia, C-100 [10], Leipzig Corpora [17], OSCAR [1], mC4 [55], MADLAD-400 [26], and HPLT [4]. These corpora are used to adapt mT5-small to Turkic text before translation fine-tuning. For bilingual fine-tuning, we combine publicly available parallel data with synthetic and mined parallel pairs. Public resources include KazParC [57], NTREX [15], FLORES+ [18], and OPUS [47]. Because direct Turkic–Turkic parallel data is highly imbalanced and not very suitable for training due to short sentence length, we additionally construct training pairs through back-translation with facebook/nllb-200-distilled-600M[11] and LaBSE-based bitext mining from multilingual book translations [16]. These data are used for fixed-target fine-tuning and transfer-matrix construction. This data setting is imperfect but realistic for low-resource Turkic MT. Since many fine-tuning pairs are synthetic, we interpret the results primarily as evidence about relative transfer structure under a controlled training pipeline, not as a claim that the absolute MT quality is optimal. We discuss this limitation explicitly in the Limitations section. 3 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. For evaluation, we use XWMT as the main benchmark because it provides comparable test pairs across the five Turkic languages [32]. We use Tatoeba [48] as a secondary benchmark to test whether donor preferences and transfer patterns remain stable across datasets. Detailed information about data collection, preprocessing, filtering, Latinization, dataset sizes, back-translation, book alignment, and evaluation-set construction is provided in Appendix A.1. 4 Methodology Continual Pretraining (CPT) We build onmT5-small[55], a 300M-parameter multilingual ex- tension of T5 pretrained with a span-corruption objective on mC4. We continue pretraining on Turkic monolingual corpora with the same objective to adapt the model to Turkic text before translation fine- tuning. This follows prior work showing that continued pretraining can improve low-resource translation performance for Uyghur and language adaptation for Turkish [29,49]. In the allCPT setting, we sample one million approximately 512-token chunks from each of the five languages. Each training sample is prepended with a language tag, such as <tr>, to preserve language identity. Fine-tuning For each fine-tuning run, we select one translation pair(i → t), whereiis the source language andtis the target language. We use explicit translation-source and translation-target tags, following the text-to-text formulation of T5-style models [37] and multilingual translation tagging conventions [19]. Each input is formatted as: <src_lang> <tgt_lang>: src sentence(1) where<src_lang>denotes the translation source and<tgt_lang>denotes the translation target. Both are one of <tr>, <az>, <uz>, <k>, and <ky>. EvaluationEvaluation is conducted in a zero-shot and fixed-translation-target setting. After fine-tuning on one translation pair(i→ t), we evaluate the model on translation pairs(j → t), where the translation target t remains fixed and j varies over the Turkic languages. Wheni ̸= j,iis the transfer source andjis the transfer target: by keeping the translation target fixed, we measure how fine-tuning oni → taffects performance on the unseen pairj → t. In other words, we measure how much the transfer sourceicontributes to the transfer targetjwhen the translation target is t. Wheni = j, the model is evaluated on the same translation pair used during fine-tuning. This is the easiest evaluation case, because the model has seen fine-tuning data for the exact source–target direction being tested. We use this as a reference score for the transfer cases where i̸= j. Recovery rate To quantify cross-lingual transfer, we use recovery rate adapted from prior transfer- analysis work [51,50]. For an evaluation metricm, letS m (i, j, t)denote the score of a model fine-tuned oni → tand evaluated onj → t, whereiis the transfer source,jis the transfer target, andtis the translation target. Recovery rate measures the percentage of performance retained when the transfer source i is different from the transfer target j for a certain translation target t. It is computed as: R m (i, j, t) = S m (i, j, t) S m (j, j, t) × 100.(2) To obtain a language-pair-level transfer score from transfer sourceito transfer targetj, we average recovery over all valid translation targets that are different from both i and j: 4 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. BLEU recovery rate (%) FT\ EvaltrazuzkkkyAvg. tr–57.1935.0326.5938.64 39.36 az 41.78–40.8230.6543.15 39.10 uz 33.0544.59–37.2042.48 39.33 k37.1542.7739.98–48.99 42.22 ky32.5438.4141.8239.32–38.02 en30.8634.1628.0829.4732.29 30.97 chrF recovery rate (%) FT\ EvaltrazuzkkkyAvg. tr–79.9070.1759.6169.55 69.81 az 71.39–73.1666.0874.47 71.28 uz 65.5573.60–71.6673.34 71.04 k66.3171.3773.35–79.87 72.73 ky63.0569.9672.4268.86–68.57 en63.1163.8762.6563.0565.17 63.57 Table 1: allCPT mT5 Latin recovery-rate transfer matrix. Rows indicate transfer sources and columns indicate transfer targets; non-diagonal cells report recovery averaged over translation targets different from both languages. The English row is a non-Turkic baseline, diagonal cells are omitted, and the Avg. column reports row-wise averages. T m (i, j) = 1 |L\i, j| X t∈L\i,j R m (i, j, t),(3) whereL =tr, az, uz, k, ky. Thus,T m (i, j)summarizes how strongly transfer sourceisupports transfer target j across possible Turkic translation targets. We also include English as a high-resource external transfer source from a different language family. English provides a useful contrast for observing how transfer behaves when the fine-tuning source is not linguistically close to the Turkic languages. For Turkic transfer sources, recovery is averaged over translation targetst ∈ L\i, j, so that the translation target differs from both the transfer sourcei and the transfer targetj. For English, this condition is relaxed because English is included only as an external transfer source and not as a translation target inL. Therefore, the English row is averaged over translation targets t∈L\j. Evaluation Metrics We report four evaluation metrics. BLEU [34] measures word-level n-gram overlap between the model output and the reference translation, while chrF [35] measures character-level n-gram overlap with an F-score. We also use neural evaluation metrics: COMET [38] is a reference-based metric that estimates translation quality using the source sentence, model output, and reference translation, whereas COMETKiwi [39] is a reference-free quality estimation metric that evaluates the model output using only the source sentence. We report all metrics consistently across the transfer-matrix experiments. 5 Experiments and Results 5.1 Cross-Lingual Transfer Matrices (RQ1) We first evaluate cross-lingual transfer in the allCPT mT5 setting, where all five Turkic languages are represented in Latin script. Using the recovery rate defined in Section 4, we construct transfer matrices where rows correspond to transfer sources and columns correspond to transfer targets. These matrices answer RQ1 by showing how transfer dynamics are shaped by the relationship between the transfer source and the transfer target. Closer Turkic pairs show stronger transfer than English.Table 1 shows that transfer strength differs clearly across transfer source–transfer target pairs. The strongest BLEU recovery appears from Turkish to Azerbaijani, where tr→az reaches 57.19%, and from Kazakh to Kyrgyz, where k→ky reaches 48.99%. The same pattern appears in chrF: tr→az reaches 79.90%, while k→ky reaches 79.87%. These pairs also align with the subgroups of the Turkic family: Turkish and Azerbaijani are both Oghuz languages, while Kazakh and Kyrgyz are both Kipchak languages. 5 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. English is included as a high-resource non-Turkic transfer source to test whether the strongest transfer results come from general high-resource training or from linguistic relatedness within the Turkic family. In BLEU, English recovers only 28.08–34.16%, which is below the strongest Turkic transfer pairs. In chrF, English is more stable, reaching 62.65–65.17%, but it still remains below the intra-Turkic pairs. This suggests that high-resource training alone does not explain the strongest transfer results, and linguistic relatedness within the Turkic family plays an important role. This is consistent with recent work suggesting that intrinsic language similarity and domain match can support cross-lingual transfer [13], with similar observations reported for Uralic languages [46]. While recent studies have established the effectiveness of cross-lingual transfer across the Turkic language family [33,56], our results further provide evidence that the degree of similarity, family subgroup proximity (e.g., within Oghuz or Kipchak branches), is associated with transfer efficiency. Kazakh is the strongest transfer source on average. The Avg. column in Table 1 summarizes the overall strength of each language as a transfer source across all transfer targets. In BLEU, Kazakh has the highest average recovery with 42.22%, followed by Turkish, Uzbek, and Azerbaijani with similar averages around 39%. The same pattern appears in chrF, where Kazakh again has the highest average recovery with 72.73%, followed by Azerbaijani with 71.28% and Uzbek with 71.04%. English has the lowest average in both metrics, with 30.97% BLEU and 63.57% chrF, showing that a high-resource non-Turkic transfer source is weaker on average than the Turkic transfer sources. Full recovery matrices for all targets and metrics are provided in Appendix A.3.1. 5.2 Translation Target Effect (RQ2) Transfer depends on the translation target. Figure 1 shows that the same transfer source–transfer target pair can produce different recovery rates depending on the translation target. When Azerbaijani is the transfer source and Kyrgyz is the transfer target, recovery changes from 35.64% with Turkish as the translation target to 48.23% with Uzbek and 45.59% with Kazakh. Therefore, transfer cannot be described only as a fixed relationship between two source languages. The translation target also shapes how much knowledge transfers from one source language to another. Transfer is directional and shaped by transfer-target–translation-target similarity. Another in- terpretation of Figure 1 is that transfer is directional: transferring from Azerbaijani to Kyrgyz is not equivalent to transferring from Kyrgyz to Azerbaijani under the same translation target. For instance, with Turkish as the translation target, az→ky recovery is 35.64%, whereas ky→az recovery is 52.49%. A similar asymmetry appears for az→k and k→az with Turkish as the translation target, where recovery increases from 32.76% to 51.01% in the reverse direction. These results suggest that recovery rate tends to be higher when the transfer target and the translation target belong to the same Turkic subgroup, either Oghuz or Kipchak. A related study suggests that similar target languages can provide stronger positive transfer in one- to-many multilingual MT by using the same translation source for the fine-tuning and evaluation pairs while varying their translation targets [31]. Our setting differs from this design: we keep the translation target fixed and reverse the transfer source–transfer target direction. Therefore, our results provide a complementary view by showing that transfer is also affected by the relationship between the transfer target and the fixed translation target. Additional transfer source–transfer target pairs are provided in Appendix A.3.2 6 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. 25303540455055 az⇄ ky, target = tr az⇄ ky, target = uz az⇄ ky, target = k az⇄ k, target = tr az⇄ k, target = uz az⇄ k, target = ky BLEU recovery rate (%) Right Direction→Left Direction← Figure 1: Paired BLEU recovery-rate comparison for mT5 Latin. Each y-axis label shows a pair of possible transfer source–transfer target directions under a fixed translation target. Direction→denotes transfer from the left language to the right language in the y-axis label, while Direction←denotes the reverse transfer direction. In the first row, right direction measures az as the transfer source and ky as the transfer target with tr as the translation target The left direction measures the reverse direction, where ky is the transfer source and az is the transfer target. 5.3 Latinization Effects on Transfer (RQ3) Latinization is a secondary but important factor because the five languages differ in script usage. Turkish and Azerbaijani are written in Latin script, Kazakh and Kyrgyz are commonly written in Cyrillic, and Uzbek is mixed in practice. Therefore, original-script experiments combine linguistic transfer with orthographic mismatch, while Latinized experiments reduce that script mismatch and make surface overlap easier for the model to use [44]. Transfer∆BLEU (%)∆chrF (%)∆COMET (%) az→k+33.00+30.81-19.04 az→ky+63.64+46.08-24.49 uz→k+41.03+64.06-24.91 uz→ky+59.63+40.79-21.27 ky→k-21.01-8.20-11.06 Table 2: Relative effect of Latinization on allCPT XWMT scores with tr as the translation target. The Transfer column denotes transfer source→transfer target. Positive values indicate that Latinization improves the score over the original-script setting, while negative values indicate a decrease. Latinization improves surface metrics for script-mismatched transfer targets. Table 2 reports percent changes from the original-script setting to the Latinized setting. The largest gains appear when the transfer target is Kazakh or Kyrgyz, which are written in Cyrillic in the original-script setting. For example, when Azerbaijani is the transfer source and Kyrgyz is the transfer target, Latinization improves BLEU by 63.64% and chrF by 46.08%. Similarly, when Uzbek is the transfer source and Kazakh is the transfer target, Latinization improves BLEU by 41.03% and chrF by 64.06%. These gains suggest that Latinization helps the model exploit surface-form similarities that are partly hidden when the transfer source and transfer target are represented in different scripts. Latinization is not uniformly beneficial across settings and metrics. ky→k row shows that La- tinization does not always improve performance: BLEU decreases by 21.01% and chrF decreases by 8.20%. This indicates that Latinization is most useful when it reduces script mismatch between transfer languages. The same rows show negative COMET deltas, which means that better surface-form overlap 7 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. does not always translate into better semantic metric scores [36,42]. We therefore treat Latinization as a factor that reshapes the matrix, especially for BLEU and chrF, rather than as a uniform improvement across all evaluation criteria. Full Latinized-minus-original matrices are reported in Appendix A.3.3. 6 Ablation Studies The previous section presented the main transfer pattern. In this section we collect correlation-based evidence showing that the transfer patterns we observe are not artifacts of a single dataset, CPT regime, or architecture. These analyses further support the reliability of the observed intra-Turkic transfer relations. The transfer patterns are mostly stable across different test datasets.We first examine the stability of transfer source preferences across XWMT and Tatoeba test datasets. For each fixed evaluation pair j → t, wherejis the transfer target andtis the translation target, we compare all models that were fine-tuned toward the same translation target languagetbut with different transfer source languages. Each transfer sourceidefines one candidate donor model, fine-tuned oni→ tand evaluated on the same pair j → t. The score obtained on this evaluation pair is treated as the donor score for language i. For example, for the evaluation pair az→tr, we compare models fine-tuned on az→tr, uz→tr, k→tr, and ky→tr, all evaluated on az→tr. The donor with the highest score is selected as the best donor for that evaluation pair. Repeating this procedure for every evaluation pair gives a donor ranking for each metric and dataset. We compare the donor rankings obtained from XWMT and Tatoeba using two criteria. Same best donor means that the highest-scoring donor is identical on both datasets for the same evaluation pair. Same full order means that the complete ranking of donors is identical across the two datasets. Since there are five target languages and four non-target evaluation sources for each target, each metric is compared over 20 donors. SettingMetricSame best donorSame full order Orig.BLEU20/2013/20 Orig.chrF20/2017/20 Orig.COMET9/206/20 LatinBLEU19/2011/20 LatinchrF20/2014/20 LatinCOMET17/2011/20 Table 3: Donor-ranking stability between XWMT and Tatoeba for noCPT mT5. “Same best donor” means that the top-ranked fine-tuning donor is the same on both datasets for a given target and evaluation source. “Same full order” means that the complete donor ranking is identical across the two datasets. Table 3 shows that BLEU and chrF donor rankings are highly stable across datasets. In the original- script setting, both metrics select the same best donor in all 20 columns; in the Latinized setting, chrF remains perfect and BLEU differs in only one column. Full-order stability is lower, but still strong for BLEU and chrF. COMET is less consistent, especially in the original-script setting, where it preserves the same best donor in only 9/20 columns. Therefore, we treat BLEU and chrF as the main signals for donor-order stability, while COMET serves as complementary evidence. Even though absolute scores differ across XWMT and Tatoeba, the highest-ranked donor usually remains the same for BLEU and chrF. This supports the view that the observed transfer structure is not specific to a single test set, but reflects a more general intra-family transfer pattern among the Turkic languages. Detailed correlation results are provided in Appendix A.3.4. 8 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. Transfer scores remain mostly correlated across back-translated training datasets. We test the effect of the back-translation model used to create the fine-tuning data on the observed transfer patterns. For this analysis, we compare model results obtained from the original NLLB-generated fine-tuning data with results obtained from a second fine-tuning dataset generated usinggoogle/madlad400-3b-mt [26]. Test setTargetMetric rBest donor XWMTazBLEU0.8844/4 XWMTazchrF0.7724/4 XWMTkkBLEU0.7964/4 XWMTkkchrF0.8434/4 TatoebaazBLEU0.7404/4 TatoebaazchrF0.5004/4 TatoebakkBLEU0.6014/4 TatoebakkchrF0.7443/4 Table 4: Stability between NLLB-based and MADLAD-based fine-tuning data for translation targets az and k.rdenotes Pearson correlation computed over all donor×evaluation cells for each target-specific matrix. Best donor reports how often the same top-scoring transfer source is selected in both settings. Table 4 shows positive Pearson correlations between NLLB-based and MADLAD-based fine-tuning matrices in all BLEU and chrF settings. The correlations are strongest on XWMT, ranging from 0.772 to 0.884, which suggests that the relative transfer scores are largely preserved when the back-translation model changes. The correlations on Tatoeba are lower, especially for chrF with Azerbaijani as the translation target, but they remain positive. This indicates that the exact score distribution is affected by the back-translation model and evaluation set, while the overall transfer pattern remains partially consistent. The best-donor agreement gives a similar but coarser signal: the top donor is preserved in almost all cases, with the only one exception. These results further support the generalizability of our findings, while future validation on human-translated data from broader domains would provide an even stronger basis for generalization. The transfer patterns are largely similar with or without CPT. We then examine how continual pretraining affects the structure of cross-source transfer. If CPT substantially changed the transfer behavior, we would expect the noCPT and allCPT settings to produce very different off-diagonal recovery patterns. Instead, Table 5 shows high off-diagonal correlations between the noCPT and allCPT settings. ComparisonMetricr off Best donor allCPT–noCPTBLEU0.96716/20 allCPT–noCPTchrF0.91517/20 allCPT–noCPTCOMET0.96411/20 allCPT–noCPTCOMETKiwi0.97715/20 Table 5: Stability of cross-source transfer patterns on Latinized XWMT.r off denotes off-diagonal Pearson correlation and best donor denotes same best donor. High off-diagonal correlation means that the relative pattern of zero-shot transfer is largely preserved. The high off-diagonal correlations in Table 5 suggest that CPT does not create a completely new transfer map. For example, allCPT–noCPT reachesr off = 0.967for BLEU and0.915for chrF. This means that CPT can change absolute scores, but the relative organization of transfer remains largely stable. Detailed allCPT-minus-noCPT matrices are provided in Appendix A.3.5. The transfer patterns are stable across encoder-decoder and decoder-only architectures.Finally, we compare the Latinized mT5 matrix with an auxiliary Qwen3 0.6B experiment. This tests whether the 9 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. raw transfer structure is specific to an encoder–decoder model or whether a similar pattern also appears in a decoder-only model. LevelMetric rρ All raw cells (80)BLEU0.9530.897 All raw cells (80)chrF0.9290.896 Off-diagonal raw (60)BLEU0.8830.784 Off-diagonal raw (60)chrF0.8200.775 Recovery rate (20)BLEU0.6490.522 Recovery rate (20)chrF0.5290.439 Table 6: mT5 Latin vs Qwen3 Latin correlations on Latinized XWMT.randρdenote Pearson and Spearman correlation coefficients, respectively. Raw donor×evaluation matrices are strongly aligned; recovery summaries are less aligned but still moderately correlated. Table 6 shows strong alignment between mT5 and Qwen3 on raw transfer matrices. For all raw cells, Pearson correlation reaches 0.953 for BLEU and 0.929 for chrF; for off-diagonal raw cells, it remains 0.883 for BLEU and 0.820 for chrF. Recovery rate correlations are weaker but still positive. This suggests that architecture changes may rescale or smooth the transfer signal, but they do not erase the family-internal structure observed in the main mT5 matrices. Full Qwen3 recovery tables are reported in Appendix A.4. 7 Conclusion This paper examines cross-lingual transfer among Turkish, Azerbaijani, Uzbek, Kazakh, and Kyrgyz through fixed-target transfer matrices. The results show that transfer within the Turkic family depends on both the transfer direction and the translation target. The strongest recovery patterns are concentrated around the Turkish–Azerbaijani and Kazakh–Kyrgyz blocks. At the same time, the same transfer source does not behave uniformly for every transfer target. Latinization provides a second source of evidence for this interpretation. In script-mismatched directions, especially those involving Kazakh and Kyrgyz, Latinization often improves BLEU and chrF, while these gains are not always mirrored by COMET. This indicates that surface-level improvements and semantic-quality estimates can diverge. Therefore, Latinization should be interpreted as a factor that reshapes transfer patterns rather than as a uniform improvement strategy. The stability analyses further support the reliability of the observed structure. Donor preferences are highly consistent between XWMT and Tatoeba for BLEU and chrF, and the off-diagonal correlations across noCPT and allCPT show that CPT mostly preserves the transfer pattern even when absolute scores change. The auxiliary Qwen3 experiment leads to a similar conclusion: raw donor–evaluation matrices are strongly correlated with the mT5 results, although recovery summaries are less aligned. Overall, these findings suggest that cross-lingual transfer is a multi-factor phenomenon shaped by the transfer source, transfer target, translation target, script representation, and model setting. Limitations The main limitation of this study is the use of mostly back-translated bilingual pairs for fine-tuning. This choice was necessary because high-quality direct parallel data between low-resource Turkic languages is limited, and manually creating a balanced human-translated dataset was outside the scope of this work. However, synthetic data can introduce artifacts from the back-translation model and may affect the absolute scores reported in the transfer matrices. For this reason, our claims focus on relative donor 10 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. preferences, matrix structure, and stability under a fixed experimental pipeline, rather than on absolute translation quality. A second limitation is that the analysis is restricted to five Turkic languages. The observed correlations suggest that the transfer structure is systematic within this family, but the same conclusions may not directly generalize to other language families with different typological, script, or resource profiles. Repeating the same fixed-target analysis on other low-resource families and on more human-translated data would be an important direction for future work. Ethical Considerations This work aims to support research on low-resource Turkic machine translation, but the resulting models should not be treated as production-ready systems. Because much of the fine-tuning data is synthetic or automatically mined, translations may contain errors, artifacts, or biases inherited from the back- translation and filtering pipeline. These risks are especially important in high-stakes domains such as legal, medical, or governmental translation. We use publicly available or automatically generated data and do not intentionally include private or personally identifiable information. However, web-derived corpora may still contain noisy or biased content. We therefore recommend that any released models or datasets be used primarily for research, accompanied by documentation of their construction process and limitations, and carefully evaluated before deployment, especially for minority-language communities where translation errors or uneven data coverage may have disproportionate effects. Licensing and Copyright. For any released data, models, or scripts, we will preserve the required attribution information and release only materials that can be redistributed under the corresponding source licenses. Our code and model releases will be distributed under the Apache License 2.0, while data releases will follow the licenses of the original sources. When a source does not permit redistribution of the original text, we will provide the processing scripts or derived metadata instead of the restricted content. This is intended to support reproducibility while respecting the intellectual property rights of the original data providers and authors. Reproducibility. To support reproducibility, we release the dataset construction scripts, Latinization rules, fine-tuning and evaluation scripts, and result matrices used in our experiments. The repository also includes the configuration files and instructions needed to reproduce the main transfer-matrix results. All reported findings should be interpreted with respect to our specific experimental setup, including the selected models, preprocessing pipeline, decoding parameters, evaluation datasets, and metric implementations. Use of Generative AI.Generative AI tools were used only to assist with language editing and improving the clarity of the manuscript. All scientific contributions, experimental design, data construction decisions, result analysis, and interpretations were conducted and verified by the authors. Acknowledgments We thank Google Cloud, Google Cloud Academic Credit Program, and TRUBA (Turkish Science e-Infrastructure) for providing the compute resources that made this study possible. 11 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. References [1]Julien Abadji, Pedro Ortiz Suarez, Laurent Romary, and Benoît Sagot. 2022. Towards a cleaner document-oriented multilingual crawled corpus. In Proceedings of the Thirteenth Language Resources and Evaluation Conference, pages 4344–4355, Marseille, France. European Language Resources Association. [2]Belen Alastruey, João Maria Janeiro, Alexandre Allauzen, Maha Elbayad, Loïc Barrault, and Marta R. Costa-jussà. 2025. Interference matrix: Quantifying cross-lingual interference in trans- former encoders. arXiv preprint arXiv:2508.02256. 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The collected raw text was cleaned through line-level filtering (removal of short, numeric, or noisy lines), paragraph reconstruction, and MD5-based deduplication. The final datasets were stored in JSONL format for each language. The amount of data collected for each language is shown in Table 7. For continual pretraining (CPT), the data was segmented into approximately 480-token chunks using thegoogle/mt5-smalltokenizer [55], while preserving sentence boundaries. Cyrillic-based languages were transliterated into their official Latin alphabet versions. LanguageNumber of ChunksFile Size Turkish69,848,795102GB Azerbaijani16,960,00025GB Kazakh6,638,02927GB Kyrgyz3,710,96213GB Uzbek8,265,19117GB Table 7: Distribution of Monolingual Data A.1.2 Bilingual Corpus Parallel corpora were obtained from three main sources: pivot-based extraction on publicly available datasets, back-translation, and open-source books available in multiple Turkic languages. Direct and pivot-based bilingual pairs were obtained from KazParC [57], NTREX [15], and FLORES+ [18], OPUS [47] including corpora such as OpenSubtitles, TED2020, and CCAligned. All parallel data underwent multi-stage filtering, including language detection via FastText [7], script normalization, removal of noisy or misaligned pairs, length ratio constraints, and deduplication. Since the collected data were highly imbalanced and contained few direct pairs between low-resource Turkic languages, synthetic parallel 17 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. data was generated via back-translation usingfacebook/nllb-200-distilled-600M[11], with quality filtering based on LaBSE [16] similarity scores and LLM-as-a-judge evaluation method. Addition- ally, parallel data was extracted from multilingual book translations using LaBSE-based bitext mining, applying both paragraph- and sentence-level alignment with cosine similarity thresholds. Comparative evaluation against LASER [3] using an LLM-based scoring framework [24] demonstrated stronger correlation for LaBSE, which was therefore used for semantic filtering (Figure 2). These results also correlate with the work by Chimoto and Bassett[9]which stated that LaBSE works better than LASER for low-resource languages with a study on African languages. The prompt given to our judge LLM (Gemini 3.1 Pro) to score the quality of the machine translation is taken from [24] and can be found below. LLM Evaluation Prompt Score the following translation from Source Language to Target Language on a continuous scale from 0 to 100, where a score of zero means “no meaning preserved” and a score of one hundred means “perfect meaning and grammar”. Source Language source: Source Sentence Target Language translation: Translated Sentence Score: (a) LaBSE Score vs. LLM Score (b) LASER Score vs. LLM Score Figure 2: Comparison of Dataset Filtering Metrics In this work, we used pairs from publicly available datasets for CPT in transfer-coefficient sampling experiments, and we combined back-translated data with book-aligned pairs to create the FT data for transfer-matrix calculations. We used all aligned book pairs and completed the FT dataset size to 100K pairs for each language using back-translation [12], following the 100K training-size setting used by Eronen et al.[13]. The number of manually curated book-aligned pairs among Turkic languages is shown in Table 8. For inference / test data we used a subset ofturkic-interlingua/turkic_xwmt test dataset [32] which contains 400 pairs between each language pairs and as the secondary test set for 18 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. correlation experiments we used a subset of Tatoeba dataset [48] which also contains 400 pairs for each language pair. Language Pair (Source-Target)Total tr-k7605 tr-az6982 az-uz2104 tr-uz1999 k-ky275 tr-ky255 Total19220 Table 8: Distribution of Book Pairs between Languages A.2 Implementation Details A.2.1 CPT and FT Scripts for mT5-small The experiments usemT5-small(300M parameter) as the base sequence-to-sequence model. Continual pretraining follows the T5 span-corruption objective: each monolingual chunk is tokenized, random spans are replaced with sentinel tokens, and the target sequence consists of the removed spans. The same CPT hyperparameters are used across all CPT scripts, as reported in Table 9. Fine-tuning uses a fixed-translation-target transfer design. For each translation target languaget, the model is fine-tuned on one translation source–target pairi→ tand evaluated on all source languages j → tfor transfer targetj ̸= t. Inputs are formatted as explicit source and target tags followed by the source sentence. The same fine-tuning and decoding hyperparameters are used across the FT scripts, and these shared settings are reported in Table 10. Because GPU resources were limited, we did not perform an exhaustive hyperparameter search and instead adopted the learning-rate setting from Yu et al. [58]. For all CPT and FT experiments, a single Nvidia A100 80GB GPU is used via Google Cloud Console Virtual Machine Instances. Fine-tuning mT5-small model with a single translation source–target pair i → ttook 1 hour 40 minutes to 2 hours and CPT with 5M total chunks each of approximately 512 CPT settingValue Base architecture google/mt5-small / local mT5-small copy ObjectiveT5 span corruption Maximum examples1,000,000 per language for allCPT Maximum token length512 Noise density0.15 Mean noise span length3.0 Training epochs1 Batch size32 Gradient accumulation1 Learning rate5× 10 −5 Weight decay0.01 Warmup ratio0.03 Optimizer adamw_torch Precisionbf16 Save policystep-based saving with save_total_limit=1 Seed42 Table 9: Shared CPT hyperparameters used across the CPT scripts. 19 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. Fine-tuning/evaluation settingValue Languages tr, az, uz, k, ky Input format <src> <tgt> source sentence Training epochs5.0 Train batch size8 Eval batch size8 Gradient accumulation4 Learning rate3× 10 −4 Weight decay0.01 Warmup ratio0.1 Schedulerlinear Validation split0.05 Max source / target length256 / 256 Generationbeam size 5, maximum length 256, early stopping Maximum test samples400 MetricssacreBLEU, chrF, COMET, COMETKiwi COMET models Unbabel/wmt22-comet-da, Unbabel/wmt22-cometkiwi-da Seed42 Table 10: Shared fine-tuning and evaluation hyperparameters used in the transfer-matrix scripts. tokens took 5 to 6 hours. A.2.2 FT and Evaluation Scripts for Qwen3 0.6B To test whether the transfer structure observed with mT5 is specific to an encoder–decoder architecture or not, we also run an auxiliary decoder-only experiment withQwen/Qwen3-0.6B. The Qwen3 experiment follows the same fixed-translation-target transfer logic as the mT5 transfer-matrix experiments: for each pivot translation target languaget, the model is fine-tuned on one donor direction (both transfer and translation source)i→ tand then evaluated on all test directionsj → twhere transfer targetj ̸= t. The resulting matrices use fine-tuning donor (transfer source) languages as rows and evaluation source (transfer target) languages as columns. Because Qwen3 is a causal language model, the translation input and target are concatenated into a single sequence. Each training example is formatted as a natural-language translation prompt followed by the reference translation: Translate from SourceLanguage to TargetLanguage: source sentence target sentence <eos> The loss is computed only on the target/completion tokens. Prompt tokens are masked with-100in the label sequence, so that they do not contribute to the training objective. During generation, the same prompt format is used, and the prompt portion is removed from the decoded output before scoring. Implementation details can be seen on Table 11. Similar to mT5, we did not perform hyperparameter search and used the Qwen3 fine-tuning learning-rate from Luo et al. [30]. For evaluation, the fine-tuned Qwen3 model is loaded once for each translation source–target run and reused across all evaluation sources (transfer targets) for that fixed translation target. The tokenizer is switched to left padding during generation, which is required for batched causal-LM decoding. Predictions are normalized for whitespace and punctuation before scoring with sacreBLEU and chrF. For each run, the script stores per-pair scores, transfer matrices, logs, and generated predictions in JSONL format. For Qwen3 FT and evaluation experiments dual Nvidia P100 16GB GPU is used via TRUBA ARF barbun-cuda HPC servers. Fine-tuning Qwen3 0.6B model with a single translation source–target pair i→ t and obtaining the evaluation results took approximately 14 hours on this GPU setup. 20 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. A.2.3 Examples From Training and Test Datasets The following examples illustrate the JSONL formats used by the scripts. Training files contain explicit source and target language fields, source and target texts, and metadata about pivoting or synthetic gener- ation. Test files follow the commontranslationdictionary format used by XWMT/Tatoeba-style datasets. "src_lang":"az","tgt_lang":"tr","src":"Cengiz Hanin hokmranligi dovrunde 1206-1227- ci iller arasinda Simali Cinde Bati Xia ve Jin Hanedani; Turkistanda Kara Hitay, Maveraunnehir; Iranda Harezm, Horasan ve Harezmsahlar, Kafkasyada Gurculer, Dest- i Kipcakdaki Rus Knezleri, Kipcaklar ve Idil Bolqarlar uzerinde seferler", "tgt ":"Cengiz Han, hukumdarligi doneminde, 1206-1227 arasinda, Kuzey Cin’deki Bati Xia ve Jin Hanedani; Turkistan’daki Kara Hitay, Maveraunnehir; Harezm, Horasan ve Iran’daki Harezmsahlar, Kafkasya’daki Gurculer, Dest-i Kipcak’taki Rus Knezlikleri, Kipcaklar ile Idil Bulgarlari uzerine seferler yapti ve imparatorlugu doneminde gerceklestirdigi hicbir savasi kaybetmedi.", "idx":0, " pivot":"tr", "nllb_model":"facebook/nllb-200-distilled-600M", "second":"none" "translation":"tr":"Kizim yurt disinda okuyor.","ky":"Kizim cet olkodo okuyt." "translation":"tr":"Artik kime inanacagimi bilmiyorum.","ky":"Emi kimge isenerimdi bilbeym." "translation":"tr":"Buyuk bir arabam var.","ky":"Menin con masinam bar." Qwen3 FT/Eval settingValue Base model Qwen/Qwen3-0.6B Model class AutoModelForCausalLM Tokenizer class AutoTokenizer Training frameworkHugging Face Trainer / TrainingArguments Fine-tuning designFixed-translation-target translation source fine-tuning, evaluated for all transfer targets Prompt format Translate from SourceLanguage to TargetLanguage: source Training sequencePrompt + target + eos Loss maskingPrompt labels set to -100; loss computed only on target tokens Training epochs3.0 Train batch size4 Eval batch size4 Gradient accumulation8 Effective batch size32 Learning rate2× 10 −5 Weight decay0.01 Warmup ratio0.1 Schedulercosine Max gradient norm1.0 Validation split0.05 Max source / target length256 / 256 Maximum generated tokens256 Generationbeam size 5, early stopping, no sampling Maximum test samples400 per evaluation pair Precisionfp16 disabled; bf16 disabled MetricssacreBLEU, chrF Seed42 Table 11: Qwen3 fine-tuning and evaluation hyperparameters used in the auxiliary decoder-only transfer experiment. 21 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. A.2.4 Example Model Outputs Table 12 shows example outputs from the allCPT Latinized XWMT evaluation directory. All examples use Turkish as the fixed translation target and the model fine-tuned onuz→tr; only the evaluation source (transfer target) changes. A.2.5 Reproducibility Statement Our GitHub repository 2 contains: • Dataset construction scripts; • Latinization scripts and rules; • CPT, fine-tuning and evaluation scripts; • HTML files that contain the full result matrices and comparison summaries. To reproduce the main mT5 transfer matrices, run the CPT checkpoint preparation step, fine-tune one model for each ordered source–target pair, and then run the fixed-target evaluation script with MAX_TEST_SAMPLES=400. For COMET and COMETKiwi, the Hugging Face token must allow access to the corresponding Unbabel checkpoints. All runs use seed 42. A.3 Detailed mT5 Results as Complementary Data A.3.1 Latinized allCPT XWMT Recovery Tables Figure 3 reports the full Latinized allCPT XWMT recovery matrices used to support the main transfer analysis. The rows of panels correspond to fixed translation targets, while the metric columns show BLEU, chrF, COMET, and COMETKiwi. Within each panel, diagonal cells report the raw same-source score for the corresponding fine-tuning/evaluation pair, and off-diagonal cells report the recovery rate obtained when the fine-tuning source differs from the evaluation source. This organization preserves the complete numerical evidence behind the averaged transfer matrix in the main paper while making the target-conditioned structure visible: strong transfer is concentrated around related-language blocks, but the same donor can behave differently depending on the fixed translation target and evaluation source. A.3.2 Translation Target Effect Figure 4 extends the target-effect analysis from the main paper by showing additional bidirectional transfer comparisons under different fixed translation targets. Each line connects two opposite transfer Eval pairSourceReferencePrediction az→trIB r@smil@ri@lav@olaraq qeyd edirl@r ki, niyy@t terrorçulara sular vasit@sil@ sızmaq da olabil@r. Niyet, teroristlerin sudan sizdirilmasi olacagi, IB yetkilileri tarafindan ek olarak not edildi. IB resmileri iptal edilebilir ki , niyet terrorçu- lara sular vasit@siyle sızmaq da olabil@r. k→trMaqsat - lañkesterge su arqyly enu , dep qosty aqparattyq agenttik. Niyet, teroristlerin sudan sizdirilmasi olacagi, IB yetkilileri tarafindan ek olarak not edildi. ̇ Ilk olarak lañkesterge su aracılı ̆ gıyla enu , olarak kurdu ̆ gu amatör agenttik. ky→tr"Indiyanınçalgındoobyurosu bildirgendey,terroristter deñizge kirü ıkmaların üyrötüp jatı ̧sat. Niyet, teroristlerin sudan sizdirilmasi olacagi, IB yetkilileri tarafindan ek olarak not edildi. Ülkede ikinci olarak, ̇ Iran’ın çalgındoo bürosu bildirdi ̆ gi , terroristler denize girdik ıkmaların üyrütüp gitti. uz→trShuningdek , maqsad terroristlar orasiga suv orqali kirib borish deya Axborot agentligi rasmiylari qo’shimcha qiladi. Niyet, teroristlerin sudan sizdirilmasi olacagi, IB yetkilileri tarafindan ek olarak not edildi. Ayrıcaamaçterroristlerarasındasu aracılı ̆ gıyla eri ̧silmesi oldu ̆ guna Güvenlik Enstitüsü resmî resmi sayısı dahil olmak üzere i ̧saret eder. Table 12: Example generated predictions from the allCPT Latinized XWMT output directory from uz→tr FT. 2 https://github.com/TurkicTransfer/Cross-LingualTransferforMachineTranslationinTurkicLanguages 22 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. tr BLEU az-truz-tr k-tr ky-tr az-tr 13.4345.2%32.8%35.6% uz-tr 55.7% 6.29 40.6%43.1% k-tr51.0%40.2%4.0648.5% ky-tr 52.5%46.1%46.3%4.04 Avg. 53.1%43.8% 39.9% 42.4% chrF az-truz-tr k-tr ky-tr az-tr 48.6475.7%71.1%73.4% uz-tr 82.4% 39.45 74.8%76.3% k-tr 79.5% 75.2%34.7085.0% ky-tr 78.7%75.2%78.7%33.25 Avg. 80.2%75.4% 74.9% 78.2% COMET az-truz-tr k-tr ky-tr az-tr 0.718280.5%71.2%67.2% uz-tr 91.0% 0.605375.1% 69.9% k-tr88.1%78.4% 0.5429 81.4% ky-tr 87.0%78.7% 81.9%0.5519 Avg. 88.7% 79.2% 76.1%72.8% COMETKiwi az-truz-tr k-tr ky-tr az-tr 0.6805 94.7%95.3%95.5% uz-tr 93.7% 0.6217 96.0%97.7% k-tr 89.2% 88.2% 0.459498.3% ky-tr 88.5% 89.4%93.4% 0.4241 Avg. 90.5%90.8%94.9%97.2% az BLEU tr-az uz-az k-az ky-az tr-az 12.8634.0%24.4%33.6% uz-az 33.9%9.17 31.3% 42.9% k-az35.8%43.0%5.5045.7% ky-az 35.8%46.6% 46.9% 5.32 Avg. 35.2%41.2%34.2%40.7% chrF tr-az uz-az k-az ky-az tr-az 47.74 70.9% 60.3%67.2% uz-az 66.8%43.7766.8% 67.9% k-az 68.9% 74.3%38.0780.6% ky-az 67.5%75.0%75.1%36.32 Avg. 67.7%73.4%67.4% 71.9% COMET tr-az uz-az k-az ky-az tr-az 0.7429 82.8% 69.7% 68.1% uz-az 103.9% 0.653373.7%66.7% k-az 98.7% 80.1%0.577677.7% ky-az 99.9% 83.1%84.2% 0.6049 Avg. 100.8%82.0% 75.9% 70.8% COMETKiwi tr-az uz-az k-az ky-az tr-az 0.6893 88.0% 92.5%91.5% uz-az 107.4%0.6324 94.5%92.0% k-az102.5%87.5%0.4760 95.5% ky-az 102.6%88.7% 93.8% 0.4610 Avg. 104.2%88.1% 93.6%93.0% uz BLEU tr-uz az-uz k-uz ky-uz tr-uz 5.59 50.5% 26.9% 38.6% az-uz 39.9%6.9929.9% 48.2% k-uz38.5%37.8% 6.95 52.8% ky-uz 34.3%34.6%24.7% 3.96 Avg. 37.6%41.0%27.2%46.5% chrF tr-uz az-uz k-uz ky-uz tr-uz 38.3175.2%54.7%67.1% az-uz 69.9% 41.5858.6% 70.9% k-uz61.8% 65.9% 40.3174.1% ky-uz 60.7%66.1%52.8%34.83 Avg. 64.1% 69.1% 55.4%70.7% COMET tr-uz az-uz k-uz ky-uz tr-uz 0.647283.0%62.8%67.5% az-uz 97.0% 0.673164.6%67.7% k-uz 97.5% 83.0%0.612174.5% ky-uz 97.6% 82.0%64.3% 0.5981 Avg. 97.4% 82.7% 63.9%69.9% COMETKiwi tr-uz az-uz k-uz ky-uz tr-uz 0.636787.2%84.3%87.2% az-uz 107.6%0.631384.0% 89.1% k-uz108.7% 92.4%0.499892.0% ky-uz 107.7% 91.4% 81.1% 0.4799 Avg. 108.0% 90.3% 83.1% 89.4% k BLEU tr-kkaz-kkuz-k ky-k tr-k 3.94 60.8%35.5%43.6% az-k38.1%5.2340.2%45.6% uz-k25.1%32.1% 8.90 41.5% ky-k 27.4%28.1%32.8%6.12 Avg. 30.2%40.3%36.2%43.6% chrF tr-kkaz-kkuz-k ky-k tr-k35.2581.7% 69.3% 74.4% az-k 69.0%39.18 72.8% 79.1% uz-k60.0%65.4%46.07 75.9% ky-k 60.9% 65.1%67.0%41.58 Avg. 63.3%70.7% 69.7% 76.5% COMET tr-kkaz-kkuz-k ky-k tr-k0.5726 93.6%90.7% 88.3% az-k83.3%0.6144 92.3%89.2% uz-k 79.5% 85.3% 0.6259 85.1% ky-k 81.5%87.0% 93.4% 0.6383 Avg. 81.4%88.6% 92.1% 87.5% COMETKiwi tr-kkaz-kkuz-k ky-k tr-k0.4548 98.2%98.4%93.2% az-k123.8%0.4844102.2% 96.6% uz-k156.4%110.1% 0.497693.6% ky-k 151.3% 119.9% 113.7%0.4472 Avg. 143.8% 109.4% 104.8% 94.5% ky BLEU tr-kyaz-kyuz-kykk-ky tr-ky 3.4460.3%35.6%28.5% az-ky 47.4%4.6837.1% 29.3% uz-ky 40.1% 45.9% 5.85 39.7% k-ky 37.2% 39.5% 36.8%6.70 Avg. 41.6%48.6%36.5%32.5% chrF tr-kyaz-kyuz-kykk-ky tr-ky 31.6282.7%70.3%63.8% az-ky 75.3%34.48 70.9% 68.5% uz-ky 69.9% 73.0%37.4473.4% k-ky 68.2%68.7%70.6% 39.41 Avg. 71.1%74.8%70.6%68.6% COMET tr-kyaz-kyuz-kykk-ky tr-ky 0.5123 93.3% 88.6%83.6% az-ky 95.6% 0.5416 90.5% 85.7% uz-ky 98.7%92.7%0.531989.4% k-ky 99.2%93.9%95.9% 0.5658 Avg. 97.8%93.3%91.7% 86.2% COMETKiwi tr-kyaz-kyuz-kykk-ky tr-ky 0.399797.0%98.7%91.7% az-ky 125.7%0.4241100.7% 92.8% uz-ky 172.8%112.7%0.4425 95.7% k-ky 180.3%123.2%115.7%0.4037 Avg. 159.6% 111.0%105.0% 93.4% diagonal raw score recovery rate Figure 3: Full Latinized allCPT XWMT recovery matrices. Rows of panels correspond to fixed translation targets and metric columns correspond to BLEU, chrF, COMET, and COMETKiwi. Diagonal cells report raw same-source scores, off-diagonal cells report recovery rates, and the Avg. row reports the average recovery for each fine-tuning source. directions for the same language pair and translation target. Large gaps between the two markers indicate directional asymmetry, while changes across rows show that the same transfer pair can behave differently when the translation target changes. These patterns support the main claim that cross-lingual transfer among Turkic languages is target-conditioned rather than reducible to a single donor–recipient similarity score. A.3.3 Nominal Deltas for Latinized - Original XWMT test dataset Raw Scores on allCPT Figure 5 reports the raw-score changes obtained by replacing original-script inputs with Latinized inputs in the allCPT XWMT setting. Positive values indicate that Latinization improves the corresponding fine-tuning/evaluation cell, while negative values indicate a decrease. The figure complements the discussion in Section 5.3 by showing that Latinization does not act as a uniform improvement mechanism. Instead, its effect is concentrated in script-sensitive directions, especially those involving Kazakh and Kyrgyz, and the magnitude of the change differs substantially across metrics. A.3.4 XWMT and Tatoeba test dataset Correlation Details Tables 13–15 provide the detailed evidence behind the cross-dataset stability analysis. Table 13 reports raw-cell Pearson and Spearman correlations between the XWMT and Tatoeba matrices, while Table 14 summarizes whether the best donor and complete donor ordering are preserved across datasets. Table 15 23 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. 2025303540455055 az⇄ ky, target = tr az⇄ ky, target = uz az⇄ ky, target = k az⇄ k, target = tr az⇄ k, target = uz az⇄ k, target = ky tr⇄ ky, target = az tr⇄ ky, target = uz tr⇄ ky, target = k tr⇄ k, target = az tr⇄ k, target = uz tr⇄ k, target = ky BLEU recovery rate (%) Right Direction→Left Direction← Figure 4: Extended appendix version of the paired BLEU recovery-rate comparison for mT5 Latin. Each y-axis label shows two opposite transfer source–transfer target directions under a fixed translation target. Direction→denotes transfer from the left language to the right language in the y-axis label, while Direction← denotes transfer in the reverse direction. gives the corresponding target-level donor-order comparisons for BLEU and chrF. Together, these results show that absolute scores may vary between benchmarks, but the donor preference structure is largely stable for surface metrics, especially BLEU and chrF. A.3.5 Nominal Deltas for noCPT-allCPT Raw Scores Figure 6 compares the Latinized XWMT raw-score matrices obtained with allCPT against the corre- sponding noCPT matrices. Positive values indicate that continual pretraining on all five Turkic languages improves a cell, while negative values indicate that the noCPT model performs better. The comparison shows that allCPT is not uniformly beneficial. The largest decreases often appear on diagonal supervised settings, including BLEU drops of−2.93for az→tr,−3.60for uz→az,−3.34for k→uz,−3.18for uz→k, and−2.15for k→ky. At the same time, several k/ky-related cells improve, such as the target=az chrF gains for k and ky (+4.34and+2.07). This pattern is consistent with the “curse of multilinguality”, where multilingual training under fixed model capacity can hurt some high-resource or already well-represented directions while benefiting lower-resource ones [8]. Because mT5-small has limited capacity, shared Turkic adaptation may help underrepresented patterns while degrading stronger supervised representations, especially on diagonal cells. A.4 Qwen3 0.6B Recovery Tables Figure 7 reports Qwen3 0.6B recovery matrices in the same fixed-target format used for the mT5 experiments. Diagonal cells give the raw same-source score, and off-diagonal cells give the recovery rate for cross-source transfer. These matrices provide architecture-level supporting evidence for the main 24 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. tr BLEU azuz k ky uz +0.02-0.22+0.48+0.65 k +0.76+0.35-0.56+0.22 ky +0.31+0.58-0.50+0.54 chrF azuz k ky uz -0.14-0.32+10.14+7.35 k +0.55+2.27-0.53-0.24 ky +0.09 +2.17-2.44+0.75 az BLEU tr uz k ky uz -0.01+0.03+0.47 +0.99 k -1.36+0.41-0.44 +0.39 ky -0.45+0.81 +0.09 +0.43 chrF tr uz k ky uz +0.04+0.16+14.52+11.22 k -3.06+1.57+0.70+1.50 ky -0.85+3.40-0.16+1.37 uz BLEU tr az k ky az +0.10-0.15+0.73+1.17 k +0.10-0.15+1.36+0.87 ky +0.19 -0.27 -0.29 +0.47 chrF tr az k ky az +0.07-0.20 +7.19 +11.42 k -1.01 -1.98+1.98 +5.08 ky +0.94 -0.06-1.06+2.17 k BLEU tr azuz ky az +0.27+0.01+1.25+0.44 uz +0.15+0.30+1.60+0.41 ky +0.34+0.48+1.48-0.11 chrF tr azuz ky az +10.25+2.30 +7.96 +1.30 uz +16.41+5.61 +4.29 +0.85 ky +18.99+17.90+19.15+0.79 ky BLEU tr azuz k az +0.39+0.69 +0.75-0.73 uz +0.46+0.73 +1.19 +0.06 k +0.30+0.63+0.83-0.44 chrF tr azuz k az +9.21 +2.48+4.27-4.17 uz +15.87+5.07+3.06-1.86 k +16.34 +9.09 +14.71-0.48 diagonal raw scorepositive deltanegative delta zero delta Figure 5: Latinized-minus-original allCPT XWMT raw-score deltas. Rows of panels correspond to fixed translation targets and metric columns correspond to BLEU, chrF, and COMET. Positive cells indicate gains from Latinization, while negative cells indicate decreases relative to the original-script setting. results: although Qwen3 and mT5 differ in model family and training formulation, the Qwen3 matrices still exhibit structured intra-family transfer rather than random behavior. The figure therefore supports that the observed transfer structure is not merely an artifact of the mT5 encoder–decoder architecture. 25 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. SettingMetricTarget N cells Pearson r Spearman rho Original BLEUtr16.000.96590.9324 Original BLEUaz9.00-0.0428-0.3000 Original BLEUuz9.000.29490.2667 Original BLEUkk9.000.74800.7667 Original BLEUky9.000.95420.8833 Original BLEUoverall52.000.28770.3401 Original chrFtr16.000.98780.9882 Original chrFaz16.000.84450.9059 Original chrFuz9.000.20970.1500 Original chrFkk9.000.01880.3333 Original chrFky9.000.93400.8167 Original chrFoverall59.000.30370.2776 Original COMET tr16.000.82360.7618 Original COMET az16.000.41990.3853 Original COMET uz16.000.44550.5294 Original COMET k9.000.54870.5000 Original COMET ky9.000.90480.8787 Original COMET overall66.000.24530.2467 Latinized BLEUtr16.000.95150.8529 Latinized BLEUaz9.00-0.0227-0.0667 Latinized BLEUuz9.000.09850.0333 Latinized BLEUkk9.000.88100.9333 Latinized BLEUky9.000.97060.8333 Latinized BLEUoverall52.000.17920.2706 Latinized chrFtr16.000.97760.9647 Latinized chrFaz16.000.88470.9176 Latinized chrFuz9.00-0.3764-0.2510 Latinized chrFkk9.000.32870.2833 Latinized chrFky9.000.89560.7833 Latinized chrFoverall59.000.15980.1403 Latinized COMET tr16.000.94800.9500 Latinized COMET az16.000.59400.7412 Latinized COMET uz16.000.41270.5706 Latinized COMET k9.000.25150.4333 Latinized COMET ky9.00-0.2085-0.0667 Latinized COMET overall66.000.20840.2733 Table 13: XWMT–Tatoeba raw-cell correlation coefficients. SettingMetricCompared columns Same best donor Same full order Same self-transfer best donor Interpretation OriginalBLEU20.0020/2013/2020/20Very stable; suitable for coefficient estimation OriginalchrF20.0020/2017/2020/20Very stable; suitable for coefficient estimation OriginalCOMET 20.009/206/205/20Unstable; use only as weak/secondary signal Latinized BLEU20.0019/2011/2019/20Very stable; suitable for coefficient estimation Latinized chrF20.0020/2014/2020/20Very stable; suitable for coefficient estimation Latinized COMET 20.0017/2011/2016/20Less stable; use only as weak/secondary signal Table 14: XWMT–Tatoeba donor-ranking stability summary. 26 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. SettingMetric Target Eval source XWMT donor orderTatoeba donor orderVerdict Latinized BLEU trazaz (13.43) > uz (7.48) > ky (7.05) > k (6.85)az (14.19) > uz (8.98) > ky (5.35) > k (5.27)same full order Latinized BLEU truzuz (6.29) > ky (2.90) > az (2.84) > k (2.53)uz (7.76) > ky (1.50) > az (1.29) > k (1.16)same full order Latinized BLEU trkkkk (4.06) > ky (1.88) > uz (1.65) > az (1.33)ky (3.31) > k (2.57) > uz (1.59) > az (1.15)different best donor Latinized BLEU trkyky (4.04) > k (1.96) > uz (1.74) > az (1.44)ky (2.15) > k (1.39) > uz (0.71) > az (0.54)same full order Latinized BLEU aztrtr (12.86) > ky (4.61) > k (4.60) > uz (4.36)tr (12.25) > ky (5.90) > uz (4.46) > k (4.37)same best donor Latinized BLEU azuzuz (9.17) > ky (4.27) > k (3.94) > tr (3.12)uz (3.54) > ky (1.49) > tr (1.21) > k (1.05)same best donor Latinized BLEU azkkkk (5.50) > ky (2.58) > uz (1.72) > tr (1.34)k (4.89) > ky (2.77) > uz (1.53) > tr (1.45)same full order Latinized BLEU azkyky (5.32) > k (2.43) > uz (2.28) > tr (1.79)ky (3.61) > k (1.99) > uz (1.50) > tr (1.16)same full order Latinized BLEU uztrtr (5.59) > az (2.23) > k (2.15) > ky (1.92)tr (4.66) > az (1.93) > ky (0.61) > k (0.48)same best donor Latinized BLEU uzazaz (6.99) > tr (3.53) > k (2.64) > ky (2.42)az (3.47) > tr (1.68) > ky (0.71) > k (0.61)same best donor Latinized BLEU uzkkkk (6.95) > az (2.08) > tr (1.87) > ky (1.72)k (6.62) > tr (1.67) > ky (1.66) > az (1.59)same best donor Latinized BLEU uzkyky (3.96) > k (2.09) > az (1.91) > tr (1.53)ky (3.85) > k (1.87) > az (1.77) > tr (1.49)same full order Latinized BLEU kktrtr (3.94) > az (1.50) > ky (1.08) > uz (0.99)tr (4.30) > az (3.65) > ky (0.63) > uz (0.51)same full order Latinized BLEU kkazaz (5.23) > tr (3.18) > uz (1.68) > ky (1.47)az (4.58) > tr (2.47) > ky (1.82) > uz (1.49)same best donor Latinized BLEU kkuzuz (8.90) > az (3.58) > tr (3.16) > ky (2.92)uz (6.55) > az (3.10) > tr (2.91) > ky (2.36)same full order Latinized BLEU kkkyky (6.12) > az (2.79) > tr (2.67) > uz (2.54)ky (3.85) > tr (1.41) > uz (1.30) > az (0.95)same best donor Latinized BLEU kytrtr (3.44) > az (1.63) > uz (1.38) > k (1.28)tr (1.57) > az (0.95) > uz (0.37) > k (0.34)same full order Latinized BLEU kyazaz (4.68) > tr (2.82) > uz (2.15) > k (1.85)az (3.18) > tr (2.15) > uz (1.12) > k (0.97)same full order Latinized BLEU kyuzuz (5.85) > az (2.17) > k (2.15) > tr (2.08)uz (5.24) > k (2.41) > tr (2.36) > az (2.06)same best donor Latinized BLEU kykkkk (6.70) > uz (2.66) > az (1.96) > tr (1.91)k (3.14) > uz (1.35) > az (1.33) > tr (0.93)same full order Latinized chrFtrazaz (48.64) > uz (40.06) > k (38.65) > ky (38.26)az (42.86) > uz (35.10) > k (32.36) > ky (31.57)same full order Latinized chrFtruzuz (39.45) > az (29.86) > ky (29.68) > k (29.66)uz (33.90) > k (22.40) > ky (22.31) > az (21.48)same best donor Latinized chrFtrkkkk (34.70) > ky (27.32) > uz (25.97) > az (24.67)k (24.47) > ky (20.40) > uz (18.59) > az (16.97)same full order Latinized chrFtrkyky (33.25) > k (28.25) > uz (25.37) > az (24.41)ky (22.50) > k (21.62) > uz (19.44) > az (18.77)same full order Latinized chrFaztrtr (47.74) > k (32.88) > ky (32.22) > uz (31.87)tr (41.10) > ky (29.47) > uz (28.82) > k (28.52)same best donor Latinized chrFazuzuz (43.77) > ky (32.83) > k (32.52) > tr (31.02)uz (32.44) > ky (24.87) > k (24.28) > tr (23.43)same full order Latinized chrFazkkkk (38.07) > ky (28.58) > uz (25.42) > tr (22.96)k (34.35) > ky (27.34) > uz (23.66) > tr (22.26)same full order Latinized chrFazkyky (36.32) > k (29.26) > uz (24.65) > tr (24.41)ky (33.68) > k (27.37) > uz (23.21) > tr (23.09)same full order Latinized chrFuztrtr (38.31) > az (26.77) > k (23.68) > ky (23.27)tr (30.43) > az (22.02) > k (17.47) > ky (17.21)same full order Latinized chrFuzazaz (41.58) > tr (31.28) > ky (27.50) > k (27.41)az (30.77) > tr (23.45) > k (21.69) > ky (21.08)same best donor Latinized chrFuzkkkk (40.31) > az (23.62) > tr (22.05) > ky (21.27)k (38.79) > az (23.83) > tr (23.30) > ky (21.74)same full order Latinized chrFuzkyky (34.83) > k (25.81) > az (24.71) > tr (23.36)ky (34.64) > k (26.66) > az (24.93) > tr (23.63)same full order Latinized chrFkktrtr (35.25) > az (24.31) > ky (21.47) > uz (21.16)tr (28.20) > az (21.08) > ky (17.11) > uz (16.60)same full order Latinized chrFkkazaz (39.18) > tr (32.02) > uz (25.64) > ky (25.50)az (35.98) > tr (29.50) > ky (25.36) > uz (24.57)same best donor Latinized chrFkkuzuz (46.07) > az (33.56) > tr (31.93) > ky (30.88)uz (40.46) > az (29.80) > tr (28.33) > ky (28.15)same full order Latinized chrFkkkyky (41.58) > az (32.87) > uz (31.54) > tr (30.92)ky (29.86) > uz (23.76) > az (23.59) > tr (22.15)same best donor Latinized chrFkytrtr (31.62) > az (23.82) > uz (22.09) > k (21.58)tr (22.67) > az (20.17) > uz (18.56) > k (18.26)same full order Latinized chrFkyazaz (34.48) > tr (28.53) > uz (25.17) > k (23.70)az (34.98) > tr (28.51) > uz (24.86) > k (23.49)same full order Latinized chrFkyuzuz (37.44) > az (26.56) > k (26.42) > tr (26.33)uz (38.02) > k (27.63) > tr (26.62) > az (26.51)same best donor Latinized chrFkykkkk (39.41) > uz (28.91) > az (27.01) > tr (25.15)k (27.55) > uz (22.96) > az (21.96) > tr (19.90)same full order Table 15: Detailed XWMT–Tatoeba donor-order comparisons for the Latinized mT5 setting using BLEU and chrF. tr BLEU azuz k ky uz -2.04-2.41+0.37-0.05 k -1.57 -0.94 -2.37-0.26 ky -1.55-0.44+0.04-1.33 chrF azuz k ky uz -1.28-2.46+3.73+1.87 k -0.30-0.47-2.02+1.64 ky -0.85-0.38+2.21-1.50 COMET azuz k ky uz -0.0270-0.0562+0.0626+0.0313 k -0.0121 -0.0259 -0.0536+0.0435 ky -0.0062-0.0216+0.0245-0.0411 COMETKiwi azuz k ky uz -0.0218-0.0468+0.0206 +0.0194 k -0.0074-0.0174-0.0305+0.0003 ky +0.0073-0.0041-0.0011 -0.0191 az BLEU tr uz k ky uz -1.60-3.60-0.18-0.60 k -1.23-0.55-3.33-0.44 ky -1.39 -0.65+0.12-2.26 chrF tr uz k ky uz -1.08-2.13+4.34+2.07 k -0.11+1.37-1.18+3.77 ky -0.57+0.18+3.62-0.23 COMET tr uz k ky uz -0.0160 -0.0659 +0.0643+0.0388 k -0.0271 -0.0195-0.0594 +0.0581 ky -0.0123-0.0176+0.0578 -0.0299 COMETKiwi tr uz k ky uz -0.0245-0.0511 +0.0192 +0.0281 k -0.0230-0.0048 -0.0299+0.0199 ky -0.0078 -0.0129 +0.0087-0.0161 uz BLEU tr az k ky az -0.61-3.13-0.44-0.36 k -0.17 -0.95 -3.34 -0.49 ky -0.54-1.32-0.71 -1.79 chrF tr az k ky az -0.54-2.70+0.80+1.22 k +0.37-1.76-4.15-0.10 ky -0.67-3.04-2.27-2.28 COMET tr az k ky az -0.0228-0.0636 +0.0190 +0.0364 k -0.0157-0.0160 -0.0692+0.0179 ky +0.0082-0.0204-0.0110-0.0534 COMETKiwi tr az k ky az -0.0304 -0.0493 -0.0062+0.0182 k -0.0247-0.0084-0.0350-0.0053 ky -0.0032-0.0110-0.0137-0.0152 k BLEU tr azuz ky az -0.67-1.80 -0.39 -0.04 uz -0.38-0.73-3.18+0.08 ky -0.27-0.63-0.10-1.82 chrF tr azuz ky az -2.12 -1.09 +1.63+4.02 uz -0.59 -1.46-1.80+3.48 ky -0.23+0.51+1.85-0.50 COMET tr azuz ky az -0.0175 -0.0059 +0.0018+0.0364 uz +0.0020-0.0145-0.0208+0.0264 ky +0.0023 +0.0098 +0.0183-0.0045 COMETKiwi tr azuz ky az -0.0132-0.0140 -0.0239 +0.0301 uz +0.0167-0.0035-0.0185+0.0248 ky +0.0196+0.0409 +0.0026 -0.0129 ky BLEU tr azuz k az -1.01-2.08-0.81-0.46 uz -0.53 -0.93 -1.87+0.26 k -0.29 -0.56-0.40-2.15 chrF tr azuz k az -2.86-2.04-0.11+0.33 uz -1.04-1.48-0.58+2.54 k -0.09 -0.06+1.88 -0.39 COMET tr azuz k az -0.0167-0.0072-0.0134-0.0603 uz +0.0092 -0.0078-0.0103 -0.0259 k +0.0078+0.0087+0.0157-0.0073 COMETKiwi tr azuz k az +0.0063-0.0130-0.0358-0.0468 uz +0.0708+0.0060 -0.0129-0.0291 k +0.0433+0.0300+0.0067 -0.0119 diagonal raw scorepositive deltanegative delta zero delta Figure 6: allCPT-minus-noCPT raw-score deltas on Latinized XWMT. Rows of panels correspond to fixed translation targets and metric columns correspond to BLEU, chrF, COMET, and COMETKiwi. Positive cells indicate gains from allCPT, while negative cells indicate stronger noCPT performance. 27 Cross-Lingual Transfer for MT in Turkic LanguagesCinar et al. tr BLEU az-tr uz-tr k-tr ky-tr az-tr 13.4343.6%21.6%25.1% uz-tr 55.5%6.5125.3%31.1% k-tr45.4%33.5%4.62 49.7% ky-tr 50.2%35.6%51.5%3.50 en-tr 39.3% 32.6%18.8%22.3% Avg. 47.6%36.3% 29.3% 32.1% chrF az-truz-tr k-tr ky-tr az-tr 48.6475.1%53.5%51.4% uz-tr 82.7% 39.7744.9% 55.5% k-tr78.3% 68.9% 35.2387.7% ky-tr 78.5% 69.2% 84.5%32.50 en-tr 72.1%64.7%26.2%23.5% Avg. 77.9%69.5% 52.3%54.5% az BLEU tr-az uz-az k-az ky-az tr-az 12.8634.1% 23.9%19.2% uz-az 34.0% 9.14 21.0%26.4% k-az46.4%38.6% 5.94 41.7% ky-az 39.4%37.9%41.9%4.89 en-az 32.3% 31.9% 15.0%20.6% Avg. 38.0%35.6%25.4%27.0% chrF tr-az uz-az k-az ky-az tr-az 47.7471.1%60.0%56.3% uz-az 66.7%43.61 29.2% 38.4% k-az75.3%71.0%37.37 79.4% ky-az 69.3% 67.5% 76.9%34.95 en-az 66.5%63.4%24.2%23.7% Avg. 69.5% 68.2%47.6% 49.5% uz BLEU tr-uz az-uz k-uz ky-uz tr-uz 5.8048.7%22.4% 16.9% az-uz 36.7%7.1424.1%21.2% k-uz35.3% 39.1% 5.59 35.0% ky-uz 29.8% 37.7%36.0% 3.49 en-uz 29.3% 35.1%21.8%21.5% Avg. 32.8%40.2%26.1%23.6% chrF tr-uz az-uz k-uz ky-uz tr-uz 38.2374.8%47.5%45.7% az-uz 69.8% 41.78 42.9% 40.7% k-uz64.6%70.3%38.3363.5% ky-uz 58.4%66.0%58.3%32.66 en-uz 57.9%61.9% 22.8%20.1% Avg. 62.7%68.2% 42.9% 42.5% k BLEU tr-kkaz-kkuz-k ky-k tr-k4.0858.2%32.7% 39.0% az-k30.1%5.22 31.9% 37.7% uz-k20.6%26.4%7.3034.2% ky-k 18.1% 19.0%19.7% 6.23 en-k17.2%15.5%15.1%26.2% Avg. 21.5% 29.8%24.9% 34.3% chrF tr-kkaz-kkuz-k ky-k tr-k33.71 79.8% 60.6%72.5% az-k41.7%36.8861.3%77.4% uz-k14.1%54.3%41.7875.2% ky-k 7.4%20.6%28.1% 40.79 en-k12.2% 19.7% 25.4% 69.9% Avg. 18.9% 43.6% 43.9% 73.8% ky BLEU tr-kyaz-kyuz-kykk-ky tr-ky 3.25 59.1% 32.0% 39.2% az-ky 38.1% 3.99 30.5%37.7% uz-ky 28.3%35.6%4.6636.4% k-ky 30.1%30.6%28.3%7.14 en-ky 24.3%32.8%21.5%33.3% Avg. 30.2% 39.5% 28.1%36.6% chrF tr-kyaz-kyuz-kykk-ky tr-ky 29.52 80.6%66.1%77.7% az-ky 49.5% 32.0064.8%78.2% uz-ky 21.1%62.8%34.3877.1% k-ky 17.8%45.7%34.1% 39.89 en-ky 15.3%30.5%30.2%76.1% Avg. 25.9%54.9% 48.8%77.3% diagonal raw score recovery rate Figure 7: Qwen3 0.6B recovery matrices. Rows of panels correspond to fixed translation targets and metric columns correspond to BLEU and chrF. Diagonal cells report raw same-source scores, off-diagonal cells report recovery rates, and the Avg. row reports average recovery for each fine-tuning source. 28

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