This study examines attitudes, reported actions and professional practices in regard to language from an occupational group that consists of ‘language experts’ − interpreters. It focuses on the topic of linguistic variation, perceptions of ‘native-speakerness’, accommodation to other languages, and nominated accounts for perceived difficulties in working with others – due to linguistic, extra-linguistic or other situational factors. The first part contextualises the sometimes separate and sometimes shared paths that characterise the standardisation of Bosnian, Croatian and Serbian and how these languages are classified formally by interpreter directories and universities in Germany and Austria. Empirical data from practising interpreters are then presented that contain responses to different features relevant to the discourse and interactional management of interpreter assignments, such as nominated first language(s) and ethnicity, perceptions of others’ designations and conceptualisations of the languages, language variant employed with ‘same-language’ vs. ‘congruent-language’ interlocutors, discourse features of German-speaking judicial officials and of allophone clients, the ‘mediator role’ of the interpreter etc.