Longitudinal study ; Erstspracherwerb; First language acquisition; Ontogenese; Language acquisition ; Dual language acquisition; Bimodal language acquisition; Spracherwerb (biling.) ; Language acquisition (biling.) ; Bilingual language acquisition ; Differenzierung (Zweisprachiger Spracherwerb) ; Differentiation (bilingual language acquisition) ; Language differentiation (bilingual language acquisition) ; Sprachenwahl; Language choice; Diglossia ; English ; French