Bilingualism; interference; Polish; Czech; language; Český Těšín region

This article is aimed at problems of language competence in actual nationally, culturally and also linguistically mixed territory of Český Těšín region in the Czech-Polish borderland in the north of the Czech Republic, where a mutual contact among Czech and Polish languages and the local dialect takes place. The article has arisen from a survey carried out by the method of questionnaire research and particular peaces of information were confronted with existent school papers written by the bilingual secondary school students from Karviná (Český Těšín region). Except the results and a questionnaire research evaluation, this work includes a short analysis of texts, which in morphological, lexical and syntactical levels deals with concrete cases of undesirable Polish-Czech interference mistakes.