Contributions of internal and external factors to bilingual development: Evidence from Kurdish-English adolescents

Aims: This study examined the role of internal and external factors in bilingual language outcomes in a societal/first language (L1) and minority/foreign language (FL) context. Methodology: Participants were 98 Kurdish-English adolescents, living in the Kurdistan Region of Iraq. The data collected through a detailed questionnaire and a battery of standardized and researcher-developed measures. Data and analysis: Data were analyzed using backward regression and hierarchical regression models. Findings: Richness of the Kurdish and English environment contributed to language outcomes, of which parental Kurdish proficiency, Kurdish input from media, and paternal English proficiency were the best predictors of greater Kurdish morphosyntactic knowledge and faster lexical access ability in Kurdish and English. Cognitive and age factors predicted language outcomes, of which nonverbal analytic reasoning and older age of English exposure were the best predictors of greater English morphosyntactic knowledge and larger vocabulary size in both languages. As two different sets, external factors outweighed internal factors in terms of vocabulary size and lexical access abilities in both languages as well as Kurdish morphosyntax. The contribution of two sets was alike for English morphosyntax. Conclusions: Sensitivity to variation in individual difference factors varies depending on the linguistic domains. External factors are more essential for bilingual development, but at the same time, the role of internal factors in dual language learning should not be underestimated. Originality: With valuable insights offered by previous research, this study contributes to the field of bilingual development through examining a large number of individual difference factors in one of the most under-studied bilingual populations.