Language Coverage Is Not Variety Coverage: Lexical Underrepresentation of Classical Chinese in Multilingual Tokenizers

Lifan Deng


Abstract
Multilingual models are commonly described as supporting Chinese, but language-level coverage may conceal disparities between historical and modern varieties. We audit five public or widely deployed tokenizer families on Classical Chinese prose and Modern Chinese newspaper text. XLM-R, a canonical multilingual representation model, requires 1.070 tokens per Classical character versus 0.688 for Modern Chinese. More importantly, only 17.4% of annotated two-character Classical words receive a single XLM-R token, compared with 66.4% of Modern words. After controlling for word length and corpus frequency, the odds of atomic coverage are 0.158 of the Modern odds. Four general-purpose LLM tokenizers reproduce the same asymmetry. Exact sentence-length matching, frequency controls, Traditional-Simplified pairs, and leave-one-source-out tests rule out several simple artifacts. Multilingual tokenizers can therefore cover a language’s script while underrepresenting the lexical units of its historical varieties.
Anthology ID:
2026.mrl-1.5
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
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
53–57
Language:
URL:
https://aclanthology.org/2026.mrl-1.5/
DOI:
Bibkey:
Cite (ACL):
Lifan Deng. 2026. Language Coverage Is Not Variety Coverage: Lexical Underrepresentation of Classical Chinese in Multilingual Tokenizers. In Proceedings of the 6th Workshop on Multilingual Representation Learning (MRL 2026), pages 53–57, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Language Coverage Is Not Variety Coverage: Lexical Underrepresentation of Classical Chinese in Multilingual Tokenizers (Deng, MRL 2026)
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PDF:
https://aclanthology.org/2026.mrl-1.5.pdf