VLT ; English as a second language; ESL; TESOL ; Wortschatz (Sprachunterricht) ; Lernwortschatz; Vocabulary teaching ; Longitudinal study ; Sprachperzeption/Sprachproduktion (Asymmetrie von) ; Language perception/language production (disparity in) ; Active vocabulary/passive vocabulary; Passive vocabulary; Disparity; Language production/language perception (disparity in) ; Zweitspracherwerb (lex.) ; Second language acquisition (lex.) ; Vocabulary (second language acquisition) ; English