In today’s world, tertiary education institutions globally are increasingly fostering international professional and academic ambitions in their students, while purposefully equipping them with the cross-disciplinary skill sets needed to turn these ambitions into transnational realities. One common way institutions pursue internationalization is by implementing English as a Medium of Instruction (EMI) in a wide range of courses across various programs. To fully understand the impact of adopting English as a scientific lingua franca and as a transnational medium of instruction in higher education, the field of EMI studies must cultivate a heightened awareness of context-specificity. This qualitative sociolinguistic research project focuses on the entanglement of English and local languages in multilingual EMI classrooms at Flemish universities, based on 10 months of linguistic ethnographic data collection in Belgium. While primarily centered on interactional data, the study also incorporates attitudinal data and field notes for triangulation. The findings highlight the role of EMI content lecturers as co-producers of micro-level language policies, which often expand the scope of institutional language policies through systematic multilingual practice.