Massive Open Online Courses (MOOCs) have become essential resources for teachers’ continuous professional development. However, beyond merely acquiring disciplinary knowledge, MOOCs provide a valuable platform for exploring teachers’ language practices, particularly in written form, within a professional context. The CERTICEscol 2023 MOOC plays a key role in teachers’ ongoing training by helping them integrate technology into their teaching practices. This MOOC, supported by UNESCO, AFD, and AUF, is designed by the University of Cergy-Pontoise and targets a broad French-speaking audience. This study examines the language practices of teachers in training through this platform, a topic often overlooked in this context. It is based on the analysis of interactions within a discussion forum and a WhatsApp group dedicated to Moroccan participants. Presented at the International Conference on “Communication and Digital Transformation,” this research falls under the second theme, which explores new forms of social interaction and language practices. This framework raises important questions about the language skills required to engage in a MOOC and the unique communication practices associated with each channel, using an approach rooted in digital ethnography. The study aims to provide insights into these questions to better understand the written language practices of teachers in online professional development and to enhance their effectiveness. It also seeks to leverage a range of group communication theories by connecting them with a new perspective on the ethnography of communication through digital use.