This tutorial paper addresses foreign-language support in corpus-based concatenative text-to-speech systems. We give an overview of application domains where strictly monolingual speech synthesis is not sufficient and where multilingual text-to-speech is required or highly desirable. We describe two approaches to multilingual corpus-based speech synthesis: phoneme mapping on the one hand, and the creation of multilingual speech databases on the other. We list the strengths and weaknesses of both approaches.