Peer Instruction (PI) has been applied widely in several institutions due to its success in supporting students' engagement and improving learning outcomes. This study examined the application of PI to an Introductory Computer Science course for year-one students taught in English that is not their native language. We aimed to identify the effectiveness of PI to improve students' content learning and English skills. Throughout the analysis of a survey of students' perceptions, we found evidence of the success of PI in terms of engagement and learning of the students, as occurred in previous studies. We found also encouraging results regarding the opportunities provided by PI to improve students non-native language skills. However, we found alarming results regarding the lack of pre-class reading preparation. Instructors should handle this issue since it is a crucial component when implementing the PI methodology for content learning and knowledge acquisition.