Comment 11 for bug 1249423

It seems that retrieving the user's default language is particularly painful on Windows and we would have to rely on GetUserDefaultUILanguage (Gimp uses it here: https://git.gnome.org/browse/gimp/tree/app/language.c?h=gimp-2-8).
Unfortunately I can't find an easier way (a function returning the equivalent of a LANG variable) to fix the issue.

If it helps, I can add a partial fix that would allow the switch code to work when the language UI is set from the Inkscape preferences (thanks to the LANGUAGE variable), but it doesn't work if it is set to System default.