Just Go Parallel: Improving the Multilingual Capabilities of Large Language Models

Muhammad Reza Qorib, Junyi Li, Hwee Tou Ng


Abstract
Large language models (LLMs) have demonstrated impressive translation capabilities even without being explicitly trained on parallel data. This remarkable property has led some to believe that parallel data is no longer necessary for building multilingual language models. While some attribute this to the emergent abilities of LLMs due to scale, recent work suggests that it is actually caused by incidental bilingual signals present in the training data. Various methods have been proposed to maximize the utility of parallel data to enhance the multilingual capabilities of multilingual encoder-based and encoder-decoder language models. However, some decoder-based LLMs opt to ignore parallel data instead. In this work, we conduct a systematic study on the impact of adding parallel data on LLMs’ multilingual capabilities, focusing specifically on translation and multilingual common-sense reasoning. Through controlled experiments, we demonstrate that parallel data can significantly improve LLMs’ multilingual capabilities.
Anthology ID:
2025.acl-long.1602
Volume:
Proceedings of the 63rd Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
Month:
July
Year:
2025
Address:
Vienna, Austria
Editors:
Wanxiang Che, Joyce Nabende, Ekaterina Shutova, Mohammad Taher Pilehvar
Venue:
ACL
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
33411–33424
Language:
URL:
https://preview.aclanthology.org/ingestion-acl-25/2025.acl-long.1602/
DOI:
Bibkey:
Cite (ACL):
Muhammad Reza Qorib, Junyi Li, and Hwee Tou Ng. 2025. Just Go Parallel: Improving the Multilingual Capabilities of Large Language Models. In Proceedings of the 63rd Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers), pages 33411–33424, Vienna, Austria. Association for Computational Linguistics.
Cite (Informal):
Just Go Parallel: Improving the Multilingual Capabilities of Large Language Models (Qorib et al., ACL 2025)
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PDF:
https://preview.aclanthology.org/ingestion-acl-25/2025.acl-long.1602.pdf