Thank you for your question Agnès Dargent! Currently Dust only supports english. Other languages will likely be supported in the future but it's not on the roadmap yet.
Note that models are multi-lingual - meaning it can take english and/or french as input and gives english and/or french as output. In other words, speaking french doesn't impact the performance of your assistants.
Please keep sharing your feedback ! They help the team understand what could bring the most value 😊