BVSLP: Enhancing Machine Translation through NMT Fine-Tuning, Back-Translation, and LLM-Assisted Synthetic Data Generation

Palak Arora, Adhikarimayum Sharma, Mrityunjaya Indoria, Keneiwenuo Lhoungu, Lalthafamkimi Lalthafamkimi, Bharti Nathani, Nisheeth Joshi


Abstract
This paper presents a two-stage neural machine translation framework for English and selected low-resource Northeastern Indian languages. The approach incorporated transfer learning, bidirectional fine-tuning, back-translation, and LLM-assisted synthetic data augmentation. In Stage 1, the NMT model was fine-tuned on cleaned gold-standard parallel data. In Stage 2, additional synthetic sentence pairs were generated using back-translation and Qwen2.5-Instruct, followed by filtering based on language identification, length ratio, duplicate removal, named-entity preservation, semantic similarity, and round-trip consistency. The framework was evaluated on English–Assamese, English–Mizo, English–Manipuri, English–Bodo, English–Khasi, and Nagamese–English translation directions. Results show stronger performance for several Northeastern-language-to-English directions, while the contrastive system notably improved Manipuri (Bengali)–English translation from 26.56 to 30.59 BLEU. The findings indicate that controlled synthetic augmentation can improve low-resource MT, although its effectiveness remains language- and direction-dependent.
Anthology ID:
2026.wmt-main.147
Volume:
Proceedings of the Eleventh Conference on Machine Translation
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Barry Haddow, Tom Kocmi, Philipp Koehn, Christof Monz
Venues:
WMT | WS
SIG:
SIGMT
Publisher:
Association for Computational Linguistics
Note:
Pages:
2086–2093
Language:
URL:
https://aclanthology.org/2026.wmt-main.147/
DOI:
Bibkey:
Cite (ACL):
Palak Arora, Adhikarimayum Sharma, Mrityunjaya Indoria, Keneiwenuo Lhoungu, Lalthafamkimi Lalthafamkimi, Bharti Nathani, and Nisheeth Joshi. 2026. BVSLP: Enhancing Machine Translation through NMT Fine-Tuning, Back-Translation, and LLM-Assisted Synthetic Data Generation. In Proceedings of the Eleventh Conference on Machine Translation, pages 2086–2093, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
BVSLP: Enhancing Machine Translation through NMT Fine-Tuning, Back-Translation, and LLM-Assisted Synthetic Data Generation (Arora et al., WMT 2026)
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PDF:
https://aclanthology.org/2026.wmt-main.147.pdf