When negotiating with partners from abroad, which language should we choose: a native or a foreign one? To answer this question, we leverage dual‐process theory to investigate how using a native versus foreign language affects negotiation strategies and outcomes and explore the moderating role of emotions. Across three studies that use dual‐language speakers of four of the five most common languages in the world (English, Chinese, Spanish and French), our findings consistently show that, while the native language is the preferred option for negotiation (Study 1), the consequences are more emotional expression, more passive strategies and worse outcomes (Studies 2 and 3). Anger in a native versus foreign language makes negotiators compromise more, which results in worse outcomes (Study 3). Our contribution is threefold: We are the first to explore the effects of language (foreign vs. native) in an empirical negotiation setting; we separate the intrapersonal from the interpersonal effects of language by using the Actor‐Partner Interdependence Model; and we establish that the language effects are independent of culture. Our results suggest that managers should use their native language with caution when negotiating, since they might unconsciously display higher levels of emotion and use more passive negotiation strategies.