Growth language mindsets (i.e., beliefs that language ability can be improved) are found to sustain learners' motivation and resilience in challenging situations. Considering that migrants who are speakers of languages other than the dominant ones often face challenging daily communications, we examined important but understudied questions of 'how' and 'when' growth language mindsets predict migrants' language experiences, including language anxiety, language use, and perceived English proficiency. In 3 studies, we surveyed 2,163 foreign-born university students in Canada who indicated English as their second language. We found that growth language mindsets positively predicted self-assessed English proficiency, even 4 months after the initial assessment of mindsets. Answering 'how,' we found that migrants with stronger growth mindsets were less anxious, were more likely to use English, and reported higher proficiency, even after accounting for baseline proficiency. Concerning 'when,' we found that mindsets have significant and moderate association with language use, anxiety, and perceived proficiency for only more recently arrived students (who lived in the receiving country for less than 7 years). Although newly arrived migrants are more anxious about using English and less likely to use English, they are resilient when they envision growth in their new language. Growth mindsets may help English as a second language (ESL) students thrive in intercultural communication and succeed in language development.