Assessing the Impact of Language Disparity on Multilingual Linguistic Ability in Large Language Models

Zhanyu Chen, Jaap Jumelet


Abstract
Claims about the grammatical competence of multilingual language models vary sharply with how competence is measured, yet the interaction between evaluation paradigm, post-training, and language resource availability has not been systematically examined. We evaluate base and post-trained models from six families on MultiBLiMP, a syntactic minimal-pair benchmark covering 101 languages, using four evaluation methods. We report three principal findings. First, post-training degrades grammatical competence, but the magnitude of this effect is determined by post-training recipe rather than model scale, and scaling reduces it unevenly, with low-resource languages bearing the highest cost. Second, post-trained models retain grammatical knowledge they cannot articulate through explicit prompting, yet this is measurable only in high-resource languages, because near-chance baselines in low-resource settings leave little knowledge to hide. Third, native-language prompting recovers otherwise hidden competence on low-resource languages, demonstrating that only high-resource languages can be probed directly from unprompted probabilities. We conclude that multilingual grammatical evaluation must adopt language-informed, multi-paradigm protocols to avoid systematically underestimating low-resource abilities.
Anthology ID:
2026.emnlp-main.337
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
7752–7776
Language:
URL:
https://aclanthology.org/2026.emnlp-main.337/
DOI:
Bibkey:
Cite (ACL):
Zhanyu Chen and Jaap Jumelet. 2026. Assessing the Impact of Language Disparity on Multilingual Linguistic Ability in Large Language Models. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 7752–7776, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Assessing the Impact of Language Disparity on Multilingual Linguistic Ability in Large Language Models (Chen & Jumelet, EMNLP 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.emnlp-main.337.pdf