This study investigates the occurrence of students' language alternation practices during second language (L2) book talk. The data were collected at a voluntary book club for learning English at a university in Korea. The book club was implemented using Zoom. In this context, using multimodal conversation analysis, I highlight instances in which students successfully construct their book talk in English (their L2) but go further by providing translations in Korean (their first language), thus doing repair to deal with (potential) problems of understanding and speaking. The findings show that through these self-repair practices of translation the student-speakers are not only (1) pursuing mutual understanding with the recipients but also (2) managing their turn construction in their doing of book talk. I argue that through these language alternation practices, the students are treating the establishment of intersubjectivity as a central activity of the book talk, which reflects their anticipation of recipients' possible difficulties in understanding the L2. The findings contribute to a better understanding of language alternation practices in a language learning context and expand our understanding of the endogenous nature of L2 book club activities conducted in a synchronous online session.