Task-Preserving Multilingual Instruction Tuning for Open-Ended QA at WMT 2026 MIST

Aleix Sant, Jordi Luque Serrano, Carlos Escolano Peinado


Abstract
We describe our submission to the WMT 2026 Multilingual Instruction Shared Task. We adapt Qwen3-8B with LoRA using organiser-provided data, EuroAlpaca, a multilingual instruction dataset created through task-preserving localisation, and CrossEuroAlpaca, a cross-lingual augmentation that assigns different source and target languages to instructions, contexts and responses. Our system targets open-ended question answering (QA-OEG) in ten shared-task languages represented in the auxiliary data. Under matched decoding, adaptation improves the mean automatic Gemma-4 judge score on target-language QA-OEG by 7.8% relative to the base model. On the 27-language Aya Evaluation Suite, it yields relative gains of 41.5% in macro-averaged ROUGE-L and 2.9% in BERTScore-F1, with larger improvements in the target languages. However, these gains are task- and language-specific. Gemma-4 scores improve for QA-OEG and summarisation in the target languages but decline for context-grounded QA within this set and across all three tasks outside it.
Anthology ID:
2026.wmt-main.132
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:
1965–1972
Language:
URL:
https://aclanthology.org/2026.wmt-main.132/
DOI:
Bibkey:
Cite (ACL):
Aleix Sant, Jordi Luque Serrano, and Carlos Escolano Peinado. 2026. Task-Preserving Multilingual Instruction Tuning for Open-Ended QA at WMT 2026 MIST. In Proceedings of the Eleventh Conference on Machine Translation, pages 1965–1972, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Task-Preserving Multilingual Instruction Tuning for Open-Ended QA at WMT 2026 MIST (Sant et al., WMT 2026)
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PDF:
https://aclanthology.org/2026.wmt-main.132.pdf