There are two timer jobs involved. One synchronizes the language setting with Active Directory, or with a non-default user profile service in some cases. That synchronization is typically not an issue.
The other is the one that controls what sites know, the "User Profile service application - User Profile to SharePoint language and region ...
About the language settings in SharePoint, you could refer to this article:
For it may take an hour to apply this setting after making changes, i think there should be a timer job running hourly to sync the language.