While translanguaging has gained increasing recognition as a multiliteracy pedagogy in English-medium instruction (EMI) education, research exploring its implementation in STEM classroom contexts remains limited. Furthermore, the interplay of EMI teachers' professional identities and their instructional strategies has received little attention. This qualitative study explores how STEM academics in an EMI programme in China implemented translanguaging pedagogy, developed their professional identities, and examined the impact of identity on their classroom instructional language use. Drawing upon nexus analysis, the study maps the intersecting discourses influencing two EMI lecturers' divergent language ideologies and translanguaging strategies. The findings highlight the role of teacher identity and agency in navigating institutional and classroom discourses, facilitating planned and effective translanguaging pedagogy. The study reveals identity struggles within the examined institution, where academic staff faced a challenge in balancing their roles as effective EMI teachers and successful researchers due to a discourse of research meritocracy and were constrained in exploring translanguaging pedagogy due to a discourse of internationalism. These challenges undermined their motivation to invest in teaching identity and pedagogical skills. This study underscores the need for a balanced view of research and teaching, more robust teacher evaluation systems, and institutional support to foster effective translanguaging pedagogy in EMI by incorporating teacher identity construction into EMI teacher preparedness.