Based on many decades of research on using multiple languages in mathematics classrooms, instructional approaches have been developed and promoted to exploit students’ multilingual resources for mathematics teaching and learning. Some of these approaches go beyond the communicative potential (to increase all students’ participation) and focus on the epistemic potential of deepening students’ understanding of mathematical concepts. However, an implementation gap exists in that only a few mathematics teachers have started to exploit this epistemic potential in their classrooms. To overcome this implementation gap, specific professional development opportunities for multilanguage-responsive mathematics teaching are required. In this paper, we lay a foundation for developing such professional development opportunities by specifying what teachers may need to learn in order to respond appropriately to typical situational demands of eliciting multiple languages for their epistemic potential. For this, we extend the existing model of expertise for language-responsive mathematics teaching by refining already identified situational demands, with respect to the epistemic potential of multiple languages.