This study examined language shift from speaking Russian to German longitudinally in a sample of 229 adolescent immigrants (Mage = 16.14, Mlength of residence = 6.26, 67% female). Our aims were to test whether language shift can be found in adolescent first generation immigrants and to test whether variables indicative of (a) linguistic adaptability, i.e., the efficiency to learn, speak and use a second language, (b) the amount of contact with native Germans, and (c) the motivation to use German, predicted differences in adolescents’ levels and rates of change in German language use. Results showed an overall decelerated increase in German language use over time, which resembled a “learning curve” leveling off at an average “frequent” use of German. Differences between adolescents in language shift were mainly associated with variables indicative of interethnic contact and motivation, but not to linguistic adaptability. In more detail, speaking German increasingly in daily life was related to an increasing share of native peers, a decreasing self-identification as Russian and an increasing orientation towards natives. Language shift thus seems to result from an increasing sense of belonging to the receiving society.