Are the LLMs Capable of Maintaining at Least the Language Genus?
Summary
Multilingual LLMs often reply in a language other than the prompt's, and their accuracy varies widely across languages. Earlier work mostly treated this as simple adherence versus deviation. This paper asks whether genealogical relatedness shapes the behaviour. The authors reanalyse MultiQ (Holtermann et al., 2024), replacing its coarse family-level grouping (English / same family / other) with WALS genera. They pose two questions:
- When a model abandons the prompt language, does it stay within the same genus?
- Does a correct answer in one language predict a correct answer in a related language of that genus?
Besides the six original open-weight models, they add the fully open Apertus-8B and generate its answers with the original MultiQ pipeline.
Genus fidelity splits the models into three clear tiers: Llama-2 lowest, Mistral/Mixtral/Qwen in the middle and Apertus highest. Genus-level effects do appear, but the amount of training data per language explains much more of the behaviour, and model families follow distinct multilingual strategies. For lower-resource languages, linguistic proximity therefore offers limited protection against data imbalance.
Key points
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Data and genus mapping: MultiQ has 27,400 parallel questions (200 per language, 137 languages).
- Languages were mapped to genera through WALS (2,662 entries) using WALS and ISO 639-3 codes.
- The result is 47 genera in 21 families. Eighteen genera contain two or more languages (101 languages in total), led by Indic (16) and Germanic, Bantu and Slavic (11 each).
-
Models and tools:
- Models: Llama-2-Chat in 7B, 13B and 70B, Mistral-7B-Instruct-v0.1, Mixtral-8x7B-Instruct-v0.1, Qwen1.5-7B-Chat and Apertus-8B. The paper's table labels the middle Llama size "14b", while the appendix uses "13b". Apertus covers about 1,800 languages, with roughly 40% non-English data.
- Answers were judged by gpt-4-0125-preview, and response languages were identified with GlotLID.
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Metric: FidelityScore is the share of prompts whose response genus equals the prompt's genus.
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FidelityScore results:
Model Score Llama-2-7B 17.3 Llama-2-13B 23.1 Llama-2-70B 27.9 Qwen1.5-7B-Chat 70.5 Mixtral-8x7B 73.9 Mistral-7B 75.0 Apertus-8B 92.3 Apertus falls to roughly 0.5 or lower only for Tano and Quechuan. High fidelity does not guarantee correct answers.
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Code: available at github.com/IDSIA-NLP/GenusPref.
Cite
@inproceedings{mitrovic2026are,
title = {{Are the LLMs Capable of Maintaining at Least the Language Genus?}},
author = {Mitrović, Sandra and Kletz, David and Dolamic, Ljiljana and Rinaldi, Fabio},
booktitle = {Proceedings of the Fifteenth Language Resources and Evaluation Conference},
year = {2026},
doi = {10.63317/38cn6xjcqa4p},
url = {https://doi.org/10.63317/38cn6xjcqa4p}
}References
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