Study abroad comes with challenges, yet it is not clear how language proficiency may longitudinally predict students' social engagement and well-being. Recent changes in international student demographics, including age decreases and increased international school backgrounds, may also affect students' well-being. This study views language as a culturally specific symbolic tool that serves cognitive, social, and emotional interactions, both interpersonal and intrapersonal. By surveying 387 international students from 14 U.S. universities over 1.5 years, this study explored the role of English proficiency in facilitating students' adaptability to psychosocial challenges and well-being. The findings suggested that both English proficiency and prior-to-admission second language educational experience predict well-being, while the latter may have afforded more nonacademic adjustment to international students' continuous social engagement. In addition, the onset of social engagement and sense of belonging showed a likely importance which highlights the value of pre-study-abroad programming for facilitating international students' continuous social engagement.