Case study (language acquisition) ; Syntactic development; Morphological development; Morphologie (Spracherwerb) ; Syntax (Spracherwerb) ; Grammatical development ; Spracherwerb (lex.) ; Language acquisition (lex.) ; Vocabulary (language acquisition) ; Dual language acquisition; Bimodal language acquisition; Spracherwerb (biling.) ; Language acquisition (biling.) ; Bilingual language acquisition ; English ; Japanese