Pré-publication, Document de travail: This paper proposes an equilibrium concept, Language-Based Expectation Equilibrium , which accounts for partial language understanding in sender-receiver cheap talk games. Each player is endowed with a privately known language competence which represents all the messages that he understands. For the messages he does not understand, he has correct but only coarse expectations about the equilibrium strategies of the other player. In general, a language-based expectation equilibrium outcome differs from Nash and communication equilibrium outcomes, but is always a Bayesian solution. Partial language competence of the sender rationalizes information transmission and lies in pure persuasion problems, and facilitates information transmission from a moderately biased sender.