This chapter explores language management at Itaipu Binacional, a hydroelectric power station on the Brazil-Paraguay border, addressing a gap in Latin American workplace language policy research. The qualitative study conducted between 2018 and 2019 analysed company documents regulating language use and observed linguistic interactions among employees in a maintenance sector. The findings reveal that Itaipu’s official policies designate Portuguese and Spanish as the administrative languages, focusing mainly on written communication and signage. However, oral communication among employees relies on intercomprehension of Portuguese and Spanish, demonstrating an effective strategy for managing multilingualism. These results highlight the interplay between “in vitro” policies (formal guidelines) and “in vivo” practices (everyday interactions), offering insights into how employees deal with linguistic diversity in a bilingual workplace. The study contributes to understanding language policies and practices in a cross-border context, with implications for similar multilingual environments.