Language teaching ; English as a second language; ESL; TESOL ; English as medium of instruction ; Wortschatz (Sprachunterricht) ; Lernwortschatz; Vocabulary teaching ; Worthäufigkeit; Häufigkeitsliste; Frequency list; Frequency (lex.) ; Word frequency ; Spracherwerb (lex.) ; Language acquisition (lex.) ; Vocabulary (language acquisition) ; English