English as a second language; ESL; TESOL ; Strategie (Lerntheorie) ; Strategy (learning theory) ; Learning strategy ; Glottodidaktik; Lehrforschung; Pädagogische Linguistik; Pedagogical linguistics; Language teaching research ; Critical period (second language acquisition) ; Alter (Einfluss auf Zweitspracherwerb) ; Age (influence on second language acquisition) ; Ultimate attainment (second language acquisition) ; Near-native competence (second language acquisition) ; AoA; Age of acquisition (second language acquisition) ; Sensitive period (second language acquisition) ; English