Translanguaging is discussed widely in the literature as a new pedagogical tool for English-medium instruction (EMI) that can challenge monolingual assumptions, mitigate English language barriers, and advocate for the full use of linguistic resources in meaning making. Different EMI lecturers have been found to hold diverse translanguaging perceptions and have adopted a variety of its functions. However, more needs to be known to close the knowledge gap between how each lecturer envisions and practices their translanguaging pedagogies, if any. Employing a qualitative method using data from semi-structured interviews and classroom observation, this study investigated three Chinese tertiary EMI engineering lecturers’ translanguaging perceptions and practices. Taken together, these three cases illustrate the complex relationship between translanguaging perceptions and practices according to their interactional (e.g., students’ difficulties in understanding full EMI), socio-cultural (e.g., the socially constructed value of full EMI), and personal factors (e.g., EMI teaching experiences). We propose that the negotiation among these three domains can promote or withhold the transfer of translanguaging perceptions into practice. We use our findings to call for EMI training programs to encourage lecturers’ reflections regarding what languages are or can be used in EMI classrooms and how and why from socio-cultural, personal, and interactional perspectives.