@gbourgaultwp It’s still not clear what you are asking. You can set the Main Broadcast Language in the Plugin Settings. This is then assigned and displayed as the default language for all Shows, and all languages assigned to a Show are listed via the Data API also. The Main Broadcast Language is also listed as the language
value in the Station Data Endpoint for the API.
If you are wanting the text strings within the Radio Station Plugin to display in another language, you need to change your WordPress Language setting, and any available language translations bundled with the plugin will be used for those strings via the in-built WordPress translation functions used throughout the plugin (this is how all plugins do it.)
If you wish to allow users to translate all your page content to a particular language, rather than just the default strings, you may need to use a translation plugin.