Challenge Track: JHARNA-MT: A Copy-Augmented Hybrid of LoRA-Tuned NLLB and Lexical SMT with Minimum Bayes Risk Decoding for Low-Resource Indic Languages

Dao Sy Duy Minh, Trung Kiet Huynh, Tran Chi Nguyen, Phu Quy Nguyen Lam, Phu-Hoa Pham, Nguyễn Đình Hà Dương, Dien Dinh, Long HB Nguyen


Abstract
This paper describes JHARNA-MT, our system for the MMLoSo 2025 Shared Task on translation between high-resource languages (Hindi, English) and four low-resource Indic tribal languages: Bhili, Gondi, Mundari, and Santali. The task poses significant challenges, including data sparsity, morphological richness, and structural divergence across language pairs. To address these, we propose a hybrid translation pipeline that integrates non-parametric retrieval, lexical statistical machine translation (SMT), and LoRA-tuned NLLB-200 neural machine translation under a unified Minimum Bayes Risk (MBR) decoding framework. Exact and fuzzy retrieval exploit redundancy in government and administrative texts, SMT with diagonal alignment priors and back-translation provides lexically faithful hypotheses, and the NLLB-LoRA component contributes fluent neural candidates. MBR decoding selects consensus translations using a metric-matched utility based on a weighted combination of BLEU and chrF, mitigating the complementary error modes of SMT and NMT. Our final system, further enhanced with script-aware digit normalization and entity-preserving post-processing, achieves a private leaderboard score of 186.37 and ranks 2nd overall in the shared task, with ablation studies confirming the contribution of each component.
Anthology ID:
2025.mmloso-1.13
Volume:
Proceedings of the 1st Workshop on Multimodal Models for Low-Resource Contexts and Social Impact (MMLoSo 2025)
Month:
December
Year:
2025
Address:
Mumbai, India
Editors:
Ankita Shukla, Sandeep Kumar, Amrit Singh Bedi, Tanmoy Chakraborty
Venues:
MMLoSo | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
114–120
Language:
URL:
https://aclanthology.org/2025.mmloso-1.13/
DOI:
Bibkey:
Cite (ACL):
Dao Sy Duy Minh, Trung Kiet Huynh, Tran Chi Nguyen, Phu Quy Nguyen Lam, Phu-Hoa Pham, Nguyễn Đình Hà Dương, Dien Dinh, and Long HB Nguyen. 2025. Challenge Track: JHARNA-MT: A Copy-Augmented Hybrid of LoRA-Tuned NLLB and Lexical SMT with Minimum Bayes Risk Decoding for Low-Resource Indic Languages. In Proceedings of the 1st Workshop on Multimodal Models for Low-Resource Contexts and Social Impact (MMLoSo 2025), pages 114–120, Mumbai, India. Association for Computational Linguistics.
Cite (Informal):
Challenge Track: JHARNA-MT: A Copy-Augmented Hybrid of LoRA-Tuned NLLB and Lexical SMT with Minimum Bayes Risk Decoding for Low-Resource Indic Languages (Minh et al., MMLoSo 2025)
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PDF:
https://aclanthology.org/2025.mmloso-1.13.pdf