Second language acquisition (language teaching) ; Zweitspracherwerb (Unterricht) ; Foreign language teaching ; Gastarbeiterkinder; Migrant workers (children of) ; Auswanderer (Kinder) ; Emigrants' children; Migrantenkinder; Aussiedler (Kinder) ; Kinder mit Migrationshintergrund; Immigrants'/Emigrants' children ; Second language acquisition (psycholing.) ; Portuguese