Forschungsgeschichte; History of linguistics ; Language teaching ; Second language acquisition (language teaching) ; Zweitspracherwerb (Unterricht) ; Foreign language teaching ; Sprachnationalismus; Nationalism (linguistic) ; Nationalismus (sprachlicher) ; Language and nationality ; Foreign language teaching policy ; English as international medium ; Sprachbewahrung; Ethnolinguistic vitality; Vitality, ethnolinguistic; Sprachwechsel; Language shift; Heritage language; Language maintenance ; English