implement SDL_GetPreferredLocales

[sanette]

Hi
would it be possible to implement SDL_GetPreferredLocales?
I realized that, while on linux/macOS you can safely rely on $LANGUAGE, $LC_ALL, etc (*)
on Windows it seems more involved. So SDL implements a quite complete answer to this, I think it would be nice to benefit from their work

(*) even this is a bit subtle, see https://www.gnu.org/savannah-checkouts/gnu/gettext/manual/gettext.html#Locale-Environment-Variables

[sanette]

ok I can do it.
do you have an idea of which section of the doc you want to insert this?