Revert "app: also localize LC_TIME to GUI language."
This reverts commit a4e65ac836.
LC_TIME format apparently does not accept the broader format with just
the lang part, for instance "fr". The region is necessary, like "fr_FR".
In our supported languages, we were mostly using lang only except for a
few langs where we support regional variants.
This makes sense as time format may be quite different depending on
regions (dates are quite different in GB vs US, though that was actually
one of the cases where we were using accurate locale format).
And the main issue is that it was not only breaking time localization.
Normal string localization (LANGUAGE) got somehow broken as well by
broken LC_TIME.
Anyway for now let's just stick to whatever OS-set time format (even
though it may differ from GIMP Preferences-set language defaults).
When we set the GUI language through Preferences, also set LC_TIME, so
that locale-aware date functions also produce the right formats.
For instance, I use this in the About dialog to format the release date
of the last version of GIMP.
If any of the locale environment variables used for UI language is set
(LANGUAGE, LC_ALL, LC_MESSAGES and LANG), do not let Windows' default UI
language override these.
Language set in GIMP preferences still have higher priority.
