This study explores English language learners' cosmopolitan language practices. Based on the concepts of cosmopolitanism (i.e., becoming a global citizen) and English as a Lingua Franca (ELF), it investigates how South Korean high school students engage in collaborative English writing practices to interact with audiences in a global writing community. Using discourse analysis of students' artifacts, this study argues that cosmopolitan language practices are beneficial for cultivating global citizenry. The findings indicate that students positioned themselves as effective communicators and meaningful collaborators for change as they developed intercultural and collaboration skills. Researchers and educators are encouraged to create opportunities for language learners to engage in cosmopolitan language practices utilizing digital technologies.