django CMS has a sophisticated multilingual capability. It is able to serve content in multiple languages, with fallbacks into other languages where translations have not been provided. It also has the facility for the user to set the preferred language and so on.
django CMS determines the user’s language the same way Django does it.
It uses the django built in capabilities for this.
Once it has identified a user’s language, it will try to accommodate it using the languages set in CMS_LANGUAGES.
If fallbacks is set, and if the user’s preferred language is not available for that content, it will use the fallbacks specified for the language in CMS_LANGUAGES.