Describing the linguistic heterogeneity of a learning group requires a set of terms for the identification oflinguistic diversity. However, these terms are not consistently used in the academic and pedagogical discourse and have multiple connotations. In this paper, we present the results of a qualitative content analysis of university teacher trainees’ written portfolios on the use of the terms in German: Erstsprache [first language], Muttersprache [mother tongue], Herkunftssprache [language of origin] and Familiensprache [home language]. Results show that the terms Erstsprache and Muttersprache are used especially frequent in relation to the learners. While Erstsprache refers primarily to language acquisition processes, the term Muttersprache does not find a clearly nuanced use overall. Furthermore, we observe a general difficulty in describing linguistic heterogeneity and the needs of individual learners without differentiating among groups of learners.