Pair and small group work is infrequently welcomed in English as a Foreign Language (EFL) classes under the assumption that students tend to use their first language (L1), which is considered detrimental to learning the new language. From sociocultural perspective, however, students’ first language is claimed to play the role of an important psychological tool and can facilitate the learning process. Hence, the current study is an investigation to examine the impact of students’ L1 use on their collaborative interaction, specifically on the construct of language-related episodes (LREs), in completing form-focused editing tasks in pairs in an EFL context. The findings show that learners’ L1 can affect their interactional talk and can play certain socio-cognitive roles such as the provision of explanations for the suggestions made in pair, helping make sense of the utterances, sharing ideas instead of unilateral solutions to linguistic problems, and assisting one another in reaching solutions to the problems at hand. The functions were seen to be all conducive to the pair members’ target language development.