A growing body of research has provided evidence for the foreign language effect on thinking, notably decision-making. Our prior work found reduction of recency effect following positive feedback in a foreign language as compared to the native tongue during even-probability gambling. However, the fundamental mechanisms underlying this effect remain unclear. The present study, therefore, aims to probe into this by engaging Chinese-English bilinguals in a functional magnetic resonance imaging version of our gambling task, which required participants to make decisions between playing and leaving equal-odds bets whilst manipulating language and valence of feedback. Results showed fewer 'play' choices following positive feedback presented in English relative to Chinese while no cross-language differences were observed after negative feedback. This valence-dependent language effect on risk-taking behaviour was supported by a language-emotion-decision neural circuit involving interplay between the right lingual gyrus, left fusiform gyrus, and right inferior frontal gyrus. Overall, our findings suggest valence-differential mechanisms of the foreign language effect in the risky decision. That is, the use of a foreign language in feedback presentation attenuates emotional reaction to positive feedback and thus diminishes subsequent risk-taking behaviour. Differently, negative counterparts seem to trigger detachment from negative emotion, leading to dissociation between feedback-encoding and decision-making.