Duolingo is one of the most popular applications used for learning foreign languages and, as such, has attracted attention of numerous scholars around the world. Majority of them, however, have focused on how the app supports English instruction. Not enough has been found about using it for mastering Polish by non-native speakers. What is more, a great deal of existing research is quantitative in character, which is why there is a growing demand for projects offering a deeper insight into the issue. The goal of this case study is to fill in this gap by providing a more detailed explanation of how Duolingo can be used for learning Polish in Taiwanese academic setting, as perceived by a female student majoring in Slavic languages whose mother tongue is Mandarin. The data obtained in a series of in-depth interviews enables a better understanding of how this highly motivated learner saw the product and its main features, with gamification, forum, and English-mediated instruction among them. Put briefly, Duolingo turned out to be useful as an addition to the regular course at school and the student demonstrated high engagement by using it almost every day. But still, more research is needed to better understand how to incorporate the app into an in-class instruction and to see what strategies of learning are efficient, so that the users can benefit even more.