What is a ‘language’? What is a ‘dialect’? Officially and politically, South Tyrol (in northeastern Italy) is an Italian–German bilingual region. The local Germanic variety spoken in the area is commonly referred to as a ‘dialect’ and therefore ‘subordinate’ to Standard German. The main aim of this dissertation is to investigate whether the community is bilingual (German–Italian) – due to socio-political distinctions and thus in line with the legal regulations – or whether it is actually trilingual (German–Italian–South Tyrolean) – due to linguistic distinctions. This dissertation contributes to the understanding of how relying only on socio-political distinctions (e.g., history, national borders) when defining the term ‘language’ can have an influence on both language acquisition processes and on educational institutions (e.g., teaching practices). The South Tyrolean dialect is used for all informal purposes: it is the language used at home, in personal domains, and in everyday activities. Standard German is the main language used within educational institutions in South Tyrol. Thus, Standard German language learning in South Tyrol is routinely compared and assumed to be largely equivalent to the acquisitional path of a German monolingual child from Germany. Although Standard German and the South Tyrolean dialect are related, they also differ from each other in various ways. One way to determine how different languages or varieties are is to test the (mutual) intelligibility of the two languages/varieties. The intelligibility-based approach used in this dissertation demonstrated that the community in South Tyrol is indeed trilingual. Based on linguistic distinctions, therefore, I will show that the dialect can be classified as a distinct language. The second empirical study in this dissertation investigated whether this ‘hidden trilingualism’ has an impact on young children’s linguistic acquisitional process by using a standardized receptive language test in Standard German. The main aim of this dissertation is to show that the problem lies in the clash between the socio-political stance and the linguistic reality