The Language of Bargaining: Linguistic Effects in LLM Negotiations

TL;DR

This study investigates how language choice influences negotiation outcomes in LLMs, revealing that linguistic framing can significantly alter results and emphasizing the importance of culturally-aware evaluation beyond English.

Contribution

It systematically isolates language effects in LLM negotiations across multiple languages, showing that language choice impacts outcomes more than model differences and varies by task.

Findings

Language choice can reverse proposer advantages.

Indic languages reduce stability in distributive games.

Language effects vary with negotiation task type.

Abstract

Negotiation is a core component of social intelligence, requiring agents to balance strategic reasoning, cooperation, and social norms. Recent work shows that LLMs can engage in multi-turn negotiation, yet nearly all evaluations occur exclusively in English. Using controlled multi-agent simulations across Ultimatum, Buy-Sell, and Resource Exchange games, we systematically isolate language effects across English and four Indic framings (Hindi, Punjabi, Gujarati, Marwadi) by holding game rules, model parameters, and incentives constant across all conditions. We find that language choice can shift outcomes more strongly than changing models, reversing proposer advantages and reallocating surplus. Crucially, effects are task-contingent: Indic languages reduce stability in distributive games yet induce richer exploration in integrative settings. Our results demonstrate that evaluating LLM negotiation solely in English yields incomplete and potentially misleading conclusions. These findings caution against English-only evaluation of LLMs and suggest that culturally-aware evaluation is essential for fair deployment.