Sprachenzählung; Demography (linguistics) ; Language census ; 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 ; Lehrerausbildung; Teacher training; Lehrerfortbildung; In-service teacher training; Teacher education ; Lehrplan; Instructional advice ; Language variation/Dialectology ; Pluricentric language ; Case study (second language acquisition) ; Zweitspracherwerb (lex.) ; Second language acquisition (lex.) ; Vocabulary (second language acquisition) ; German