For multinational corporations, the need for efficiency and control has motivated the choice for a corporate language. However, increasing internationalisation has forced corporations to rethink their language policies to cater to the changing demands of the multicultural and multilingual workplace. This paper explores two related issues. First, it addresses the influence of mode of communication (English as a Lingua Franca [ELF] vs. L1-L2 interactions) on task efficiency. Second, it investigates the use of communication strategies in the different types of interactions (ELF vs. L1-L2). In a within-subject experimental design, the present study explores the effectiveness of language use in dyadic, computer-mediated communication between non-native speakers of English (ELF) and native and non-native speakers of German and Dutch (L1-L2). In three consecutive chat sessions, 60 participants performed a problem-solving task in English, German or Dutch. Findings indicate that in L1-L2 interactions, the participants were more effective in realising communicative goals than in ELF interactions, and that participants made use of different communication strategies in L1-L2 interactions than in ELF interactions. Consequently, international organisations which implement a corporate language may benefit from condoning multilingual practices on the work floor.