In recent decades, recruiting foreign professors (FPs) has become a noticeable trend at South Korean higher education institutions (HEIs) as they attempt to internationalize. However, little scholarly attention has been paid to the question of what is actually happening in classrooms as a result of this rapid influx of FPs and the associated proliferation of English-only courses. The aim of this study is to understand internationalization's real impacts on teaching and learning by examining professor-student interactions and instructional practices in a so-called "internationalized" university course (i.e., an English-speaking Canadian professor's computer architecture course for domestic Korean students). I adopt the theoretical lens of sustainability framed within an ecological perspective and focus on languages and cultures in the HEI context, while resisting market-based HEI internationalization driven by economic considerations. This study finds that Prof. Dave's course was characterized by linguistic and cultural reciprocity and equitable relations among the participants, revealing its vast potential for sustainable internationalization. Further, the course acknowledged and empowered various funds of student knowledge, including content knowledge, English capability, and Korean capability, which led to fun and effective learning. Although this successful symbiosis suggests a promising future for sustainable internationalization in Korean HEIs, I also highlight the pressing need for institution-level programs or services to assist both FPs and domestic students in FP courses.