Evaluation criterion (language teaching) ; Sprachandragogik; Volkshochschule; Adult language teaching ; Second language acquisition (language teaching) ; Zweitspracherwerb (Unterricht) ; Foreign language teaching ; DaF; Deutsch als Zweitsprache; German as a second language; DaZ; German as a foreign language ; Reciprocal language course ; Techniques (in research) ; Research techniques ; German