Comment 26 for bug 803858

Sadly, it is really anoying of not having this option set default... Here's a good reason for hat:

At my office, for multiple reasons, we are using KDE into our operational environment. We have a full french/english setup and KDE allows to switch between both languages perfectly fine BUT:

There is no way to force GTK applications to also run in the language choosen by the user unless it internally has specific options for it. Therefore, if the system wide language is set to english, french users will have to manually set the language into OpenOffice (since it does have such option) while they will have to be stuck with an english firefox & gimp & mostly every other gtk apps. Same goes the other way around... Since the user using the desktop is never the same each day, the language varies depending of who's sitting at that specific desk all the time. So we are stuck at having one of the two languages not fully functional.

How can I properly get around this issue without having a language chooser at the login screen that will set all background locales properly at login time?

For this specific reason I am strongly suggesting for a return of this option into GDM as it was default and working well in previous ubuntu releases up until this is finally set by default into lightdm:
https://bugs.launchpad.net/gdm/+bug/1015114