Mobile technologies and mobile learners have transformed the way people learn languages. In particular, they give rise to a new form of language learning: the use of online language learning platforms, a kind of virtual learning environment that offers learning opportunities that are mobile, social and multimodal (Jones and Hafner, 2012; Richards, 2015). While existing research has tended to focus either on the benefits of using mobile technologies in the teaching and learning of languages or on how mobile learners, who have different linguistic and cultural backgrounds, harness the benefits of technologies to learn new languages, few studies address both perspectives. This paper reports on a study of self-directed language learning in online platforms. In particular, I explore how mobile technologies such as online language learning platforms shape the learning practices of mobile learners, and how mobile learners take advantage of the affordances of these online platforms to achieve their learning goals, in the context of learning Chinese as a foreign language. Through in-depth analyses of two case studies, I argue that while mobile technologies seem to encourage a clear distinction between online and offline learning, in reality the boundary is less clear-cut as mobile learners bring with them a set of offline learning practices from their own experiences to the online environment. A more critical view therefore has to be taken when researching online and offline learning practices.