This study explores the motivation of five university students who simultaneously studied L2 English and additional L3s (Chinese, Japanese and Korean) in a language specialist major in a Thai university. It aims to start filling the gap in research on the motivation of multiple language learners across their different languages. The findings show that while English did threaten some learners' motivation to study other foreign languages (FLs), it also encouraged them to study other FLs. Learners of multiple FLs developed unique motivational systems in which the interrelationships of multiple motivations were dynamic and complex. Students' motivation to study other FLs was mainly generated by the immediate need and the imagined future use of that particular language.