Reinforcement Learning Elicits Contextual Learning of Unseen Language Translation

Hanxu Hu, Zdenek Snajdr, Pinzhen Chen, Jannis Vamvas, Rico Sennrich


Abstract
Prior work has shown that large language models (LLMs) can translate unseen or low-resource languages by undergoing continued training or even by encoding a grammar book in their context. However, both methods typically treat specific languages, with limited zero-shot transfer at test time. To translate extremely low-resource languages at scale, we argue that a model should be able to use in-context linguistic knowledge regardless of language, rather than memorize specific training languages. In this paper, we propose a reinforcement learning (RL) approach to unseen language translation given rich linguistic context, using a surface-level translation metric as the reward. Empirically, despite the lightweight reward, our RL-trained models effectively extract and apply relevant linguistic information from the provided context, leading to better translations on completely unseen languages than in-context learning or supervised fine-tuning. Our analyses suggest that outcome-based RL can extend beyond conventional reasoning tasks like math and coding to serve as a recipe for low-resource translation from linguistic context.
Anthology ID:
2026.findings-emnlp.2096
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
44643–44657
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.2096/
DOI:
Bibkey:
Cite (ACL):
Hanxu Hu, Zdenek Snajdr, Pinzhen Chen, Jannis Vamvas, and Rico Sennrich. 2026. Reinforcement Learning Elicits Contextual Learning of Unseen Language Translation. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 44643–44657, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Reinforcement Learning Elicits Contextual Learning of Unseen Language Translation (Hu et al., Findings 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.findings-emnlp.2096.pdf