One of the most widely pursued goals in dialogue system development is the improvement of usability, which is mainly achieved by providing users with both friendly and manageable interfaces. The MIMUS dialogue system supports multimodal interactions, allowing the user to interact not only verbally but also graphically. In addition to this, MIMUS (MultIModal, University of Seville) is a multilingual system that enables the user to communicate (dynamically) in Spanish and English. The present paper describes the MIMUS architecture, the components that entail direct relationship with multilinguality, and the way in which languages can be dynamically switched within a single dialogue.