@Ronald, thanks for your response. My intention is to integrate with an existing setup where users already have an application that maintains all language dictionaries for toggling between languages.

For example, if a user has Chinese set in their language dictionary, all captions and messages in the Mendix app should be displayed in Chinese. Similarly, if the user has German configured, the content should appear in German. If no specific language is configured for a user, the app should default to English. Could you please help in this regard ?

As Ronald mentioned already, it is possible to set the language of the user

But there are lot to do also in Mendix

1. Add all possible languages
   • Its not possible to dynamically add a language to the Mendix app
2. Set the translations
   • When new language is added, the translations for captions and messages must be set in mendix app and deployed. 
   • https://docs.mendix.com/refguide/translate-your-app-content/
3. When the language is available in Mendix, you can set the language of a user from external apps
   • NOTE: when the user is logged in already, adding, removing or changing language does not reflect. User must be logged out and logged in again.

OK thanks