The Cost of Asking in Turkish: Prompt Language Effects on Code LLMs

Mert İncidelen, Melike Kaya, Elif İşbilir, Yunus Santur


Abstract
Large language models (LLMs) have demonstrated strong performance on existing code generation benchmarks. However, these benchmarks are almost entirely based on English prompts. This study examines the cost of prompt language on code generation performance for Turkish, an agglutinative and morphologically rich language. For this purpose, EN-TR CodeBench, a benchmark consisting of 60 problems and 811 unit tests at easy, medium, and hard difficulty levels, was created. Five open-source code LLMs from three model families, one with three different parameter scales, were evaluated under English, Turkish, and Turkish-localized conditions using the pass@1 metric. The results show that the use of Turkish prompts leads to a performance decrease in all five models, and this decrease narrows as model scale increases within the Qwen2.5-Coder family. Analysis according to difficulty level reveals that, for most models, the language-related performance loss increases substantially with problem complexity. Error analysis shows that the performance difference between languages is largely driven by runtime and logic errors, while syntax errors remain rare.
Anthology ID:
2026.mrl-1.39
Volume:
Proceedings of the 6th Workshop on Multilingual Representation Learning (MRL 2026)
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
David Ifeoluwa Adelani, Jesujoba Alabi, Catherine Arnett, Tyler Chang, C.M. Downey, Omer Goldman, Senyu Li, Lester James Validad Miranda, Jirui Qi, David Stap, Genta Indra Winata, Xinyu Crystina Zhang
Venues:
MRL | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
492–496
Language:
URL:
https://aclanthology.org/2026.mrl-1.39/
DOI:
Bibkey:
Cite (ACL):
Mert İncidelen, Melike Kaya, Elif İşbilir, and Yunus Santur. 2026. The Cost of Asking in Turkish: Prompt Language Effects on Code LLMs. In Proceedings of the 6th Workshop on Multilingual Representation Learning (MRL 2026), pages 492–496, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
The Cost of Asking in Turkish: Prompt Language Effects on Code LLMs (İncidelen et al., MRL 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.mrl-1.39.pdf