Drawing on usage-based approaches this paper addresses the challenge of capturing EMI teachers' linguistic needs for the purposes of teacher training in international Medical Education. The focus is on EMI medical teachers in various instructional formats. Each format requires a specific linguistic repertoire resulting dynamic interactions of linguistic, didactic, and intercultural competence, which is difficult to define in linguistic modules such as syntax and lexicon. Moreover, a generic native speaker standard of language proficiency is questionable in this ELF context. Capturing the relevant EMI competence as linguistic units that can be taught in teacher training programs is therefore a challenge. The paper builds on central tenets shared by a number of usage-based approaches to propose that linguistic units of EMI competence can be conceptualized as highly specific language functions arising from a specific EMI instructional context and mapping onto suitable formulations in ELF. This conceptualization was applied in a local teacher training initiative. First, subject-specific language functions were identified through a combined analysis of the EMI instructional context and the teachers' instructional practices. Second, the identification procedure formed a starting point for a collaborative teacher training program. Third, a policy document was drafted, taking into account institutional limitations.