English as a second language; ESL; TESOL ; GERS; CEFR; Quadro Comune Europeo di Riferimento; Common European Framework of Reference for Languages ; Glottodidaktik; Lehrforschung; Pädagogische Linguistik; Pedagogical linguistics; Language teaching research ; Cross-cultural pragmatics; Pragmatics, cross-cultural; Pragmatik, interkulturelle; Intercultural communication ; English