I need to know what language is used in edit/admin pages.
Im trying to call EPiServer.Personalization.EPiServerProfile.Current.Language but it only returns an empty string.
You're using the correct property, but it will return an empty string if selected value from dropdown is "Use system language".
See:
http://labs.episerver.com/en/Blogs/Mari-Jorgensen/Dates/112298/2/Reflect-user-language-in-custom-properties-and-plugins/