Beyond Accuracy: A Structured Error Analysis of Multilingual LLMs on Marathi Script Variation and Syntax

Evaluation of multilingual large language models has grown rapidly in recent years, yet Marathi, spoken by over 83 million people across India, has received almost no systematic probing beyond surface-level benchmark tests. Most existing multilingual evaluations either omit Marathi entirely or rely on machine-translated test sets that fail to capture the morphological complexity that defines the language. We evaluate four models, namely Llama-3.1-8B, Llama-3.3-70B, Mistral-7B, and Qwen3-32B, on our manually curated Marathi dataset across three probing dimensions: Devanagari versus Romanized script, Marathi-English code-mixing, and syntactic structures including SOV word order, vibhakti case markers, verb gender agreement, and postpositions. Models are tested under English and Marathi instruction conditions across translation, similarity, grammaticality, and case marker tasks. Translation quality is evaluated using both token-level F1 and BERTScore to capture paraphrase equivalence beyond surface word overlap. All models drop between 7.9% and 20.5% on Romanized input. The negative subjunctive marker nasta is ignored by every model. Vibhakti case markers are consistently replaced with Hindi equivalents, revealing that multilingual training has not produced separate internal representations for Hindi and Marathi despite their distinct morphological systems. These findings reveal structural gaps in how current multilingual LLMs handle morphologically rich, low-resource Indic languages and point to specific areas where dedicated Marathi pretraining data would most benefit future work.