The internationalisation of higher education has led to widespread adoption of English as a medium of instruction in European universities, and this strategy is supporting increasingly diverse student mobility. Many students undertaking short-term Erasmus+ mobility see this as an opportunity to develop their English language skills but may lack interest in learning locally significant languages. However, contemporary universities are complex multilingual spaces. This paper explores how far mobile students' language affiliations are aligned to languages' wider geopolitical significance, and how far they are influenced by personal and sociocultural factors, and the study abroad (SA) experience itself. The study draws on a corpus of narrative interviews with mobile students in diverse European settings. Participants generally sustained strong affiliations with English. Affiliations with other international languages were more mixed. Some expressed a heightened affiliation to their home language arising from SA experience; others described new affiliations arising from local contacts and student friendships, with a local language, or with other international students' L1. Overall, the study found that language affiliations showed some flexibility, and might derive from personal biographical factors, cultural values and personal relationships as well as from the instrumental value of internationally significant languages.