With the deepening of cross-national exchange, the significance of ethnic psychology and its interdisciplinary applications has become increasingly evident. Ethnic psychology, which examines the psychological traits and behavioral patterns shaped by distinct cultural contexts, provides valuable insights into how learners from different backgrounds engage in second language acquisition. This study integrates the theoretical framework of ethnic psychology into second language acquisition research by investigating the relationship between emotional intelligence and second language grit among university students from diverse cultural backgrounds. Drawing on data from questionnaires and semi-structured interviews with 831 English learners in China and Indonesia, the study examines cross-cultural variations and correlations. Results show that Chinese students report significantly higher emotional intelligence, while Indonesian students exhibit greater second language grit. These differences are shaped by factors such as rigidity and linguistic distance. Emotional intelligence is positively correlated with second language grit in both groups, though the strength of this relationship and its predictive mechanisms vary. Cultural rigidity and time orientation (long-term vs. short-term) emerge as key influencing variables. This research underscores the value of ethnic psychology in advancing global educational equity and cooperation, offering important implications for culturally responsive educational policy, pedagogical design, and inclusive development in global English language education.