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Gains from trade generate prosperity, yet interpersonal exchange can falter along racial lines. We examine this failure in incentivized experimental economies where participants must spontaneously initiate and sustain trading relationships with others whose race is visible. When the highest gains from trade require cross-race exchange, diverse economies underperform: welfare and specialization decline as many retreat toward autarky. This underperformance stems not from segregation into racial trading blocs, but from a collapse in exchange. Exchanges diminish and performance gaps emerge, persist, and widen over time. Communication data show that lower welfare co-varies with less voluminous dialogue characterized by less talk of motivational drives (affiliation, achievement) and transparent state-signaling (needs, deficits, surpluses). We conceptualize this as communicative misalignment: observable, interactional patterns, within a shared language, that raise the costs of search, bargaining, and enforcement. A brief linguistic intervention equipping participants with a communicative toolkit increases communication volume, the targeted categories, and conversational scaffolds (verbs, function words). When cross-race exchange yields economic gains, the intervention closes the performance gap by restoring specialization and diverse trade; its minimal effects otherwise indicate that it alleviates this specific misalignment rather than teaching generic language or trading skills. Language thus operates bidirectionally. It both reveals the state of cooperation and causally shapes it. Although we examine racial boundaries, the mechanism can operate along any fault line where interactional norms diverge (e.g., culture, hierarchy, geography). As the primary conduit of culture, language can impede exchange at baseline but facilitate it when aligned. The intervention offers a scalable micro-governance tool that reduces transaction costs.