Internationalisation is a buzzword in European higher education, and many universities work hard to devise and implement strategies that will help facilitate increased transnational student mobility. In this context, English is commonly seen as the "natural" choice for university internationalisation, and English is accordingly promoted as the "obvious" language of instruction for international education in many university policies. This article argues that the idea that university internationalisation should equal the exclusive use of English as a lingua franca is essentially misguided. Not only is it at odds with the available empirical evidence, it also puts unnecessary constraints on the potential that transnational education holds for cultural and linguistic exchange and development. The article is based on a case study where the patterns of language choice of three student project groups at an international study programme in Denmark were analysed quantitatively and qualitatively. The analysis shows that although there is a quantitative preference for English in the three groups which matches the general pro-English language ideology at the programme, the groups have nevertheless, to varying degrees, developed practice-based language policies "from below" that allow for alternating and sometimes syncretic use of English and Danish.