Speak Beyond English: Multilingual Prompts Improve Query Classification in Small Language Models

Abstract

With recent advancements, Small language models (SLMs) are increasingly used as preprocessors to handle query classification, routing, and candidate selection in retrieval pipelines, but they are nearly always prompted in English, even when users search in Hindi, Bengali, or code-mixed forms. We test whether prompting the same (frozen) SLM in three typologically diverse languages and aggregating the outputs can improve classification without retraining or translation. Nine decoder-only models (1B--9B parameters) evaluated on four public benchmarks show that confidence-weighted fusion of English, Hindi, and Bengali predictions raises macro-F1 by 3--5 points over English-only baselines, with the strongest gains on binary and coarse intent tasks. Parallel execution keeps latency within 1.2--1.4× of the single-language baseline. A paraphrase-only ensemble under identical conditions reaches only +1.4~F1 on average, suggesting that cross-lingual diversity rather than surface-level input variation drives the gain. Because no additional data, training, or translation services are required, our method may be useful when scaling to larger models is out of reach.