There are no official requirements with regard to the language settings on the client side - only the browser version is a prerequisite.
I assume if you ask Cisco, they would say only english and japanese versions are tested. But this does not mean very much because it will not affect the stability of the application if you try and use other language versions on the client side. Most of the customers I know are using a german browser version to access LMS. And if you would have any issues it would be easy to change the language settings and see if this is the reason. Just try and see if it works.
