Is it possible to change language for edit and admin modes when you have multiple sites so that each site has a differente language for the CMS? I know it's possible to set this per user, but I haven't found where to change it for the entire site.
It may be worth having a read of the official documentation: http://world.episerver.com/documentation/Items/Developers-Guide/EPiServer-CMS/8/Globalization/Determining-languages/
The system language is generally set in the <globilization> element of web.config which is common to all sites so you may need to do some customisation via setting Thread.CurrentThread.CurrentUICulture per site.
Thanks for your reply David!