localize() in inkex.py ignores $LANG from current env on Windows

[su_v]

The localize() function in inkex.py to initialize gettext for messages returned by extension scripts seems to ignore $LANG from the current environment on Windows, and overwrites the environment variable with the locale apparently retrieved from the system settings:

        import locale
        current_locale, encoding = locale.getdefaultlocale()
        os.environ['LANG'] = current_locale

Tested on Windows 10:

1) set LANG in the CMD shell before launching inkscape:

C:\Users\su_v\Programs\inkscape> set LANG=de_CH
C:\Users\su_v\Programs\inkscape> inkscape

--> Inkscape's GUI shows with German localization as expected.

2) Launch a second Inkscape instance from within inkscape [*]:

--> GUI language and locale of second instance falls back to en_US (like the system settings).

Reproduced with Inkscape 0.91 (32bit, 64bit), 0.92.1 (32bit, 64bit) and inkscape_trunk_r15113 (64bit) on Windows 10, all versions installed from 7z into custom location and launched from CMD shell.

Notes:
* See also the lengthy discussion in bug #1662531 about the crash of the second inkscape instance (reported separately in bug #1663697 as well) for another issue related to localize() on Windows and a proposed improvement attached in comment https://bugs.launchpad.net/inkscape/+bug/1662531/comments/64
* Possibly locale.getdefaultlocale() was designed to work differently on Windows compared to other platforms, but it sort of feels unexpected (at least to me):
1) set LANG in CMD shell to a locale different from system settings
2) launch python\python.exe as bundled with Inkscape on Windows
3) import os, locale
3) print os.environ['LANG']
4) print locale.getdefaultlocale()
It seems that Python's locale module on Windows ignores LANG from the environment (unlike e.g. python on OS X, and unlike Inkscape itself).
Python documentation:
https://docs.python.org/2/library/locale.html#locale.getdefaultlocale

=====
[*] debug extension to spawn second Inkscape instance:
    https://gitlab.com/su-v/lp1662531

[su_v (suv-lp)]

Why is it necessary to change $LANG in the environment on Windows at all? A quick test with 0.92.1 r15371 (64bit, 7z) on Windows 10 shows translated error messages from extensions even if line 57 is commented out:

        # os.environ['LANG'] = current_locale

https://bazaar.launchpad.net/~inkscape.dev/inkscape/0.92.x/view/15371/share/extensions/inkex.py#L57

@jazzynico - do you happen to remember why you had to add it for translations of messages from extensions scripts on Windows?

[Patrick Storz (ede123)]

Is $LANG set on Windows at all? I don't think so...

Therefore if the parent Inkscape process does not set it, it will be unset. Maybe that's why we try to set it manually there?

[Patrick Storz (ede123)]

P.S. That's probably also the reason why Python ignores the variable on Windows.