> Is this the same as the other issue where get_locale is normalising 
> the result according to some particular glibc logic and isn't at 
> all portable? 

If I understand Anders' immediate problem correctly, I think it can be addressed by using setlocale() to save and restore the current locale in the calendar and _strptime modules. This requires no changes to the locale module, let alone the complete rewrite that's required to make getlocale(), normalize(), _parse_localename(), and _build_localename() work reliably in Windows.

It's not just a Windows problem. For example, getlocale() doesn't return the POSIX locale modifier in a 3-tuple (language, encoding, modifier). So it can't be used to restore a locale for which the modifier is mandatory.

The following example in Linux uses Serbian, a language that's customarily written with both the Cyrillic and Latin alphabets (i.e. BCP 47 / RFC 5646 language tags "sr-Cyrl-RS" and "sr-Latn-RS"). The Latin-based Unix locale name uses a "latin" modifier.

Say the process is currently using the Latin-based locale, but I need the name of a weekday in Cyrillic:

    >>> locale.setlocale(locale.LC_TIME, 'sr_RS.UTF-8@latin')
    'sr_RS.UTF-8@latin'
    >>> c = calendar.LocaleTextCalendar(locale='sr_RS.UTF-8')
    >>> c.formatweekday(1, 10)
    '  уторак  '

LocaleTextCalendar() temporarily sets LC_TIME to the given locale and then restores the previous locale. But this is based on the getlocale() result, which omits the "latin" modifier. So now my current LC_TIME locale has changed to Cyrillic:

    >>> locale.setlocale(locale.LC_TIME)
    'sr_RS.UTF-8'

A related problem with modifiers affects getdefaultlocale(). For example, in Linux:

    $ LC_ALL=sr_RS.UTF-8@latin python -q
    >>> import locale, calendar

In this case, the LC_ALL environment variable specifies the Latin-based locale, but getdefaultlocale() omits this important detail:

    >>> locale.getdefaultlocale()
    ('sr_RS', 'UTF-8')

Based on the default locale set in the LC_ALL environment variable, the following is supposed to return the Latin name "utorak", not the Cyrillic name "уторак":

    >>> c = calendar.LocaleTextCalendar()
    >>> c.formatweekday(1, 10)
    '  уторак  '

If I make it call setlocale(LC_TIME, '') instead of getdefaultlocale(), I get the right result:

    >>> c = calendar.LocaleTextCalendar(locale='')
    >>> c.formatweekday(1, 10)
    '  utorak  '

Thus an empty string should be the default locale value in LocaleTextCalendar(), instead of getdefaultlocale().