BSC Submission for WMT26 General Machine Translation Shared Task

Audrey Mash, Jonathan Ayebakuro, Ella Bohman, Xixian Liao, Francesca De Luca Fornaciari, Maite Melero


Abstract
We present the BSC submission to the WMT26 General Machine Translation shared task: a 7B decoder-only model covering 23 directions, adapted from the SALAMANDRA (Gonzalez-Agirre et al., 2025) family through vocabulary replacement, two rounds of continued pre-training (monolingual, followed by instruction-formatted parallel data), supervised fine-tuning on a translation-only instruction mixture, and preference optimisation applied selectively to six weak directions via CPO-SimPO (Xu et al., 2024; Meng et al., 2024) with LoRA adapters (Hu et al., 2021). Submissions are decoded with Minimum Bayes Risk selection over a candidate pool filtered for truncation, degeneracy and off-target script. As official human evaluation was unavailable at the time of writing, we report a stage-wise internal evaluation on FLORES+ and WMT24++, together with automatic scores for the submitted system on the 12 test-set directions for which references have been released. Instruction tuning accounts for almost all measurable gain, but its size differs by an order of magnitude between the two evaluation sets; preference optimisation moves automatic metrics by less than the drift among untreated directions. The model is released under a Research-Only Licence and is available on request.
Anthology ID:
2026.wmt-main.72
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:
1327–1343
Language:
URL:
https://aclanthology.org/2026.wmt-main.72/
DOI:
Bibkey:
Cite (ACL):
Audrey Mash, Jonathan Ayebakuro, Ella Bohman, Xixian Liao, Francesca De Luca Fornaciari, and Maite Melero. 2026. BSC Submission for WMT26 General Machine Translation Shared Task. In Proceedings of the Eleventh Conference on Machine Translation, pages 1327–1343, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
BSC Submission for WMT26 General Machine Translation Shared Task (Mash et al., WMT 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.wmt-main.72.pdf