Restore the old behaviour of wxLocale, which is supposed to use the
default locale and not the preferred language, which may not be the same
(see #22281).
Also apply the following fixes and improvements to wxUILocale:
- Add new GetSystemLocale() method.
- Change the MSW implementation to use the default locale instead of the
preferred UI language for Windows versions below Windows 10.
- Change the Unix implementation to respect LANGUAGE environment
variable and use it for determining the preferred UI languages.
- Use wxUILocale in wxTranslations to determine the preferred UI
languages.
- Use wxUILocale during initialization of internat sample.
Closes#22281.
Closes#22318.
8ab635b451