This interdisciplinary research examines how Informal Digital Learning of English (IDLE) and the L2 Motivational Self System (consisting of "the ideal L2 self" and "the ought-to L2 self") are linked with Foreign Language Enjoyment (FLE). Together, these are flourishing research areas in computer-assisted language learning, second language acquisition and positive psychology. Using a purposive sampling technique, three cohorts of English-as-a-foreign-language learners (N = 661) are surveyed in South Korea: middle school (n = 173), high school (n = 374) and university students (n = 114). Results of hierarchical regression analyses show that "IDLE" and "the ideal L2 self" are significantly predictive of all groups' FLE, while "the ought-to L2 self" predicts only middle school students' FLE. These results suggest that students' engagement in extramural digital activities and their motivational mindset (shaped through different socio-educational contexts) may have influenced their emotions in learning their target language. Informed by these results, teachers can help increase students' L2 learning enjoyment by supporting their language learning in out-of-class digital settings as well as promoting their ideal L2 self-images. Concurrently, teachers and parents can enhance younger learners' enjoyment of learning L2--especially in test-oriented Asian contexts--by setting higher L2 learning expectations.