English as a second language; ESL; TESOL ; Glottodidaktik; Lehrforschung; Pädagogische Linguistik; Pedagogical linguistics; Language teaching research ; Gesture communication ; Classroom communication; Instructional communication ; Triggering (language acquisition) ; Language exposure (language acquisition) ; Input hypothesis; Input (language acquisition) ; Second language acquisition (pragm.) ; Zweitspracherwerb (pragm.) ; Interactionist hypothesis (second language acquisition) ; Conversational analysis (second language acquisition)