DaF; Deutsch als Zweitsprache; German as a second language; DaZ; German as a foreign language ; Idioms (language teaching) ; Wortschatz (Sprachunterricht) ; Lernwortschatz; Vocabulary teaching ; Phraseologie; Idioms; Phraseology ; Festes Syntagma; Feste Wortverbindung; Set phrase; Fixed expression ; Semantic fields ; German