Locale names should always include the codeset component

If you install Ubuntu in English with Tel Aviv as the timezone location, the installer figures out that the applicable locale is en_IL and adds the line

LANG="en_IL"

to /etc/default/locale.

en_IL is a perfectly fine locale name; actually it's *the* correct name of the English/Israel locale for UTF-8 according to SUPPORTED. However, Python does not agree. Python seems to generally presuppose that locale names include the codeset component, even if it accepts locale names without codeset if they are included in the hard coded dictionary locale_alias in /usr/lib/python3.5/locale.py. However, en_IL is a relatively new locale, and not (yet) included in locale_alias:

gunnar@gunnar-ubuntu-current:~$ python3
Python 3.5.2+ (default, Sep 22 2016, 12:18:14)
[GCC 6.2.0 20160927] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import locale
>>> locale.setlocale(locale.LC_CTYPE, 'en_IL')
'en_IL'
>>> mylocale = locale.getlocale(locale.LC_CTYPE)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.5/locale.py", line 577, in getlocale
    return _parse_localename(localename)
  File "/usr/lib/python3.5/locale.py", line 486, in _parse_localename
    raise ValueError('unknown locale: %s' % localename)
ValueError: unknown locale: en_IL
>>> quit()

I got to know about this issue via <http://askubuntu.com/q/854950>. Now, the problem is not limited to en_IL. New locales in glibc tend to be UTF-8 only locales without the codeset included in their names in SUPPORTED. glibc and Python will probably never be in sync.

One way to deal with this issue is to always add '.UTF-8' to such locale names. For instance, 'en_IL.UTF-8' is understood by both glibc and Python.

Probably this should be fixed in localechooser. Basically I'd like to see a code snippet along these lines:

if [ "$LOCALE" = "${LOCALE%.*}" ]; then
    LOCALE=$( echo $LOCALE | sed -r 's/([^@]+)/\1.UTF-8/' )
fi

I haven't prepared a patch, since I don't know where exactly it should be inserted without breaking anything else. (Don't know how to test it either.) Still hoping that somebody finds it important enough to fix.