This qualitative case study investigates how translanguaging practices emerge during game-based learning (GBL) tasks in an online English corner for adult Chinese EFL learners. Drawing on video-recorded classroom interaction from six sessions, questionnaires, and semi-structured interviews, the study examines how learners and teachers strategically deploy bilingual (multilingual) resources during collaborative gameplay. The findings show that translanguaging served three main functions: relational (building rapport and reducing anxiety), cognitive (supporting meaning-making and problem-solving), and metacognitive (reflecting on language use and learning strategies). These practices were closely shaped by game design features such as challenge–skill balance, feedback, learner control, and social interaction. The study demonstrates that GBL creates interactional conditions that legitimise flexible language use and position translanguaging as a pedagogical resource rather than a compensatory strategy. It contributes to applied linguistics and TESOL by linking translanguaging theory with game design principles and by offering insights for designing inclusive, linguistically flexible learning environments.