I assume you're referring to Windows environment variables. I need most of my software to function trouble free in German, so this doesn't seem to be a workable solution for me, if I'm understanding you correctly.
As for the complete list under the share/locale folder ... It would be good to get a better pointer where this folder is. I certainly can't find anything of the sort on my system. I'm a programmer, and all system files are visible on my system, so I do know most of the usual places where such things would be, but I haven't been able to find anything.
GIMP does have a local user folder called ENV, but it's empty on my machine.