This quasi-experimental study investigated the efficacy of an 8-week, gamified pronunciation instructional framework grounded in Self-Determination Theory (SDT). Utilizing an explanatory sequential mixed-methods design, the study examined changes in English intelligibility, comprehensibility, and Intercultural Communicative Competence (ICC) among 116 non-English major university students in Vietnam, divided into an experimental group and a control group. Quantitative analyses via ANCOVA revealed that the experimental cohort achieved significantly higher post-test speech intelligibility and comprehensibility scores, alongside profound shifts toward global linguistic empathy regarding World Englishes. Furthermore, psychometric scales indicated substantial drops in classroom boredom and oral communication anxiety. Qualitative thematic analysis of semi-structured interviews corroborated these outcomes, demonstrating that quest-based tasks and collaborative team scenarios successfully satisfied learners' basic psychological needs for autonomy, competence, and relatedness. This research provides a systematically validated pedagogical blueprint for seamlessly integrating linguistic development with cross-cultural pragmatic awareness within modern language learning curricula.