Given the controversies surrounding the critical period hypothesis on second-language (L2) learning outcomes, this study focuses on the phonological aspect of language acquisition—the strength of the foreign accent in L2. Drawing on data from a large-scale representative data set on immigrant adolescents in Germany—CILS4EU-DE—we first demonstrate that there is a critical period (CP) up to the age of around 10, after which obtaining oral language skills without a foreign accent becomes less likely. Second, we provide evidence that native-like language skills can be achieved after the CP if certain preconditions related to learning efficiency and language exposure are met. Our analyses indicate that higher cognitive abilities and exposure to a language environment with intensive and manifold contacts with native speakers can compensate for disadvantages caused by a late start in L2 acquisition. The results are discussed in the context of the linguistic and sociological scholarship of language acquisition and immigrant assimilation.

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