This paper presents some difficulties with the teaching issue of the varieties of the contemporary Czech language in teaching process. The paper is focused on the competition between standard and non-standard varieties of Czech language when teaching Czech as a foreign language. It concerns especially the situation of the Czech colloquial language so called “obecná čeština”, sometimes considered as a specific case of language diglossia. One of the main aims is to discuss the appropriateness of using a colloquial language when teaching Czech as a foreign language, so when a student of Czech language, learning only standard language, meets with nonstandard Czech, it would not lead to a complete misunderstanding.