More Capable, Less Faithful: A Multilingual Analysis of Mathematical (Un)Solvability Detection in LLMs

Maria-Eleni Zoumpoulidi, Nikolaos Xiros, Georgios Paraskevopoulos


Abstract
Solvability detection is one of the most challenging aspects of mathematical reasoning for Large Language Models (LLMs). While prior work has studied this capability extensively, these analyses have been limited to English. Consequently, it remains unclear whether multilingual failures arise from differences in internal Solvability Belief or from language-dependent failures to express it. To address this gap, we introduce the first multilingual benchmark of paired solvable and unsolvable mathematical problems, extending ReliableMath to French and Greek. Using this, we train multilingual probes predicting Solvability Belief and analyze the solvability detection capabilities of state-of-the-art LLMs behaviorally, representationally, and in terms of faithfulness. We find that Solvability Belief is encoded as a largely universal, language-agnostic feature, and that higher-resource languages such as English, despite achieving stronger mathematical reasoning performance, exhibit lower solvability-detection faithfulness.
Anthology ID:
2026.mrl-1.6
Volume:
Proceedings of the 6th Workshop on Multilingual Representation Learning (MRL 2026)
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
David Ifeoluwa Adelani, Jesujoba Alabi, Catherine Arnett, Tyler Chang, C.M. Downey, Omer Goldman, Senyu Li, Lester James Validad Miranda, Jirui Qi, David Stap, Genta Indra Winata, Xinyu Crystina Zhang
Venues:
MRL | WS
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Publisher:
Association for Computational Linguistics
Note:
Pages:
58–67
Language:
URL:
https://aclanthology.org/2026.mrl-1.6/
DOI:
Bibkey:
Cite (ACL):
Maria-Eleni Zoumpoulidi, Nikolaos Xiros, and Georgios Paraskevopoulos. 2026. More Capable, Less Faithful: A Multilingual Analysis of Mathematical (Un)Solvability Detection in LLMs. In Proceedings of the 6th Workshop on Multilingual Representation Learning (MRL 2026), pages 58–67, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
More Capable, Less Faithful: A Multilingual Analysis of Mathematical (Un)Solvability Detection in LLMs (Zoumpoulidi et al., MRL 2026)
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PDF:
https://aclanthology.org/2026.mrl-1.6.pdf