Why do migrants choose some destinations over others? This study explores government language policy and the role of language differences in migration decisions. While governments can use language policy to reduce communication barriers, vernaculars remain critical in terms of regional communication and identity recognition. Using a survey experiment and econometric analyses of nationally representative data from China, the authors examine the communication and cultural roles of language in migration decisions in the context of a unifying common national language. The empirical tests find that migrants prefer destinations where local vernacular languages are more similar to their own, despite a common national language. Once migrants have moved, a common national language helps migrants communicate and therefore remain in their migration destinations, but it does not eliminate the role of the local vernacular as a cultural marker. The result is that both the common language and local vernacular matter for domestic migration, even in a country where the government has promoted a single common language for six decades. The findings have far-reaching implications for migration policy and citizenship management in general.