cs.CLApr 2, 2026

GaelEval: Benchmarking LLM Performance for Scottish Gaelic

Authors: Peter Devine, William Lamb, Beatrice Alex, Ignatius Ezeani, Dawn Knight, Mícheál J. Ó Meachair, Paul Rayson, Martin Wynne

Organizations: University of Edinburgh · Lancaster University · University of Cardiff · Dublin City University · 

Abstract

Multilingual large language models (LLMs) often exhibit emergent 'shadow' capabilities in languages without official support, yet their performance on these languages remains uneven and under-measured. This is particularly acute for morphosyntactically rich minority languages such as Scottish Gaelic, where translation benchmarks fail to capture structural competence. We introduce GaelEval, the first multi-dimensional benchmark for Gaelic, comprising: (i) an expert-authored morphosyntactic MCQA task; (ii) a culturally grounded translation benchmark and (iii) a large-scale cultural knowledge Q&A task. Evaluating 19 LLMs against a fluent-speaker human baseline (n=30n=30), we find that Gemini 3 Pro Preview achieves 83.3%83.3\% accuracy on the linguistic task, surpassing the human baseline (78.1%78.1\%). Proprietary models consistently outperform open-weight systems, and in-language (Gaelic) prompting yields a small but stable advantage (+2.4%2.4\%). On the cultural task, leading models exceed 90%90\% accuracy, though most systems perform worse under Gaelic prompting and absolute scores are inflated relative to the manual benchmark. Overall, GaelEval reveals that frontier models achieve above-human performance on several dimensions of Gaelic grammar, demonstrates the effect of Gaelic prompting and shows a consistent performance gap favouring proprietary over open-weight models.

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