You are correct, there isn't a specific setting within the Developer console to directly add additional languages like French. The way Google handles multiple languages for Smart Home Actions has changed. You no longer explicitly define each language in the console itself.
Instead, Google relies on the user's device settings. If a user has their Google Assistant and device language set to French, and your Action is properly designed, Google's systems will automatically attempt to use French for interactions. This means you don't submit separate versions for certification for each language.
