Student L2 motivation in Vietnamese English-Medium Instruction classrooms: a complex dynamic systems analysis

English-Medium Instruction (EMI) motivation research suffers from theoretical fragmentation and Western cultural bias that inadequately address student experiences in non-Western educational contexts. This study investigates motivational patterns among Vietnamese EMI students through Complex Dynamic Systems Theory, examining how contextual factors shape motivational dynamics in culturally distinct settings. A sequential explanatory mixed-methods design recruited 322 undergraduate students from three Vietnamese universities. Quantitative data collection employed adapted L2 Motivational Self System scales and contextually developed instruments, while qualitative semi-structured interviews with 45 purposively selected participants explored emergent patterns. Cluster analysis identified four distinct motivational profiles: Integrative-Intrinsic Learners (28.3%), Instrumentally-Driven Achievers (31.7%), Socially-Oriented Learners (24.2%), and Amotivated Strugglers (15.8%). Findings reveal that Vietnamese cultural values – particularly collectivism, hierarchical respect, and face-saving concerns – fundamentally moderate motivational orientations differently from Western contexts. Pedagogical quality, peer dynamics, and instructor rapport emerged as interactive contextual factors amplifying motivational patterns. These results challenge the universal applicability of Western-derived motivation theories in Asian EMI contexts and demonstrate the necessity of culturally grounded theoretical frameworks. Findings inform culturally responsive EMI pedagogy and advance understanding of motivation as a culturally embedded, dynamically evolving phenomenon in multilingual educational settings.