Cold Starts and Hard Cases: A Two-Stage SFT-RLVR Approach for Legal Machine Translation (Just-NLP L-MT shared task)

Pawitsapak Akarajaradwong, Chompakorn Chaksangchaichot


Abstract
This paper details our system for the JUST-NLP 2025 Shared Task on English-to-Hindi Legal Machine Translation. We propose a novel two-stage, data-centric approach. First, we annotate the training data by translation difficulty and create easy and hard subsets.We perform SFT on the easier subset to establish a robust “cold start”. Then, we apply RLVR exclusively on the harder subset, using machine translation metrics as reward signals. This strategy allowed our system to significantly outperform strong baselines, demonstrating the capability of our systems for machine translation tasks. Source code and model weights are available at https://github.com/ppaolong/FourCorners-JustNLP-MT-Shared-Task
Anthology ID:
2025.justnlp-main.9
Volume:
Proceedings of the 1st Workshop on NLP for Empowering Justice (JUST-NLP 2025)
Month:
December
Year:
2025
Address:
Mumbai, India
Editors:
Ashutosh Modi, Saptarshi Ghosh, Asif Ekbal, Pawan Goyal, Sarika Jain, Abhinav Joshi, Shivani Mishra, Debtanu Datta, Shounak Paul, Kshetrimayum Boynao Singh, Sandeep Kumar
Venues:
JUSTNLP | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
101–106
Language:
URL:
https://preview.aclanthology.org/ingest-ijcnlp-aacl/2025.justnlp-main.9/
DOI:
Bibkey:
Cite (ACL):
Pawitsapak Akarajaradwong and Chompakorn Chaksangchaichot. 2025. Cold Starts and Hard Cases: A Two-Stage SFT-RLVR Approach for Legal Machine Translation (Just-NLP L-MT shared task). In Proceedings of the 1st Workshop on NLP for Empowering Justice (JUST-NLP 2025), pages 101–106, Mumbai, India. Association for Computational Linguistics.
Cite (Informal):
Cold Starts and Hard Cases: A Two-Stage SFT-RLVR Approach for Legal Machine Translation (Just-NLP L-MT shared task) (Akarajaradwong & Chaksangchaichot, JUSTNLP 2025)
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https://preview.aclanthology.org/ingest-ijcnlp-aacl/2025.justnlp-main.9.pdf