The LegISTyr Test Set: Investigating Off-the-Shelf Instruction-Tuned LLMs for Terminology-Constrained Translation in a Low-Resource Language Variety

Paolo Di Natale, Egon W. Stemle, Elena Chiocchetti, Marlies Alber, Natascia Ralli, Isabella Stanizzi, Elena Benini


Abstract
We investigate the effect of terminology injection for terminology-constrained translation in a low-resource language variety, with a particular focus on off-the-shelf instruction-tuned Large Language Models (LLMs). We compare a total of 9 models: 4 instruction-tuned LLMs from the Tower and EuroLLM suites, which have been specifically trained for translation-related tasks; 2 generic open-weight LLMs (LLaMA-8B and Mistral-7B); 3 Neural Machine Translation (NMT) systems (an adapted version of MarianMT and ModernMT with and without the glossary function). To this end, we release LegISTyr, a manually curated test set of 2,000 Italian sentences from the legal domain, paired with source Italian terms and target terms in the South Tyrolean standard variety of German. We select only real-world sources and design constraints on length, syntactic clarity, and referential coherence to ensure high quality. LegISTyr includes a homonym subset, which challenges systems on the selection of the correct homonym where sense disambiguation is deducible from the context. Results show that while generic LLMs achieve the highest raw term insertion rates (approximately 64%), translation-specialized LLMs deliver superior fluency (∆ COMET up to 0.04), reduce incorrect homonym selection by half, and generate more controllable output. We posit that models trained on translation-related data are better able to focus on source-side information, producing more coherent translations.
Anthology ID:
2025.termtrends-1.1
Volume:
Proceedings of the 5th Conference on Language, Data and Knowledge: TermTrends 2025
Month:
September
Year:
2025
Address:
Naples, Italy
Editors:
Katerina Gkirtzou, Slavko Žitnik, Jorge Gracia, Dagmar Gromann, Maria Pia di Buono, Johanna Monti, Maxim Ionov
Venues:
termtrends | WS
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Publisher:
Unior Press
Note:
Pages:
1–15
Language:
URL:
https://aclanthology.org/2025.termtrends-1.1/
DOI:
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Cite (ACL):
Paolo Di Natale, Egon W. Stemle, Elena Chiocchetti, Marlies Alber, Natascia Ralli, Isabella Stanizzi, and Elena Benini. 2025. The LegISTyr Test Set: Investigating Off-the-Shelf Instruction-Tuned LLMs for Terminology-Constrained Translation in a Low-Resource Language Variety. In Proceedings of the 5th Conference on Language, Data and Knowledge: TermTrends 2025, pages 1–15, Naples, Italy. Unior Press.
Cite (Informal):
The LegISTyr Test Set: Investigating Off-the-Shelf Instruction-Tuned LLMs for Terminology-Constrained Translation in a Low-Resource Language Variety (Di Natale et al., termtrends 2025)
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https://aclanthology.org/2025.termtrends-1.1.pdf