This work-in-progress paper presents a specialized language corpus UcebKo built from textbooks of Czech for foreigners. The corpus integrates three subcorpora (UcebKo-A2, UcebKo-B1, and UcebKo-B2) which allow research of Czech as a second/foreign language at chosen language levels (A2, B1, and B2). In this case, the research is focused on word-formation, where the first results, i.e., mapping of derived words denoting persons, illustrate the approach and methodology used.