On Windows 10 version 1903, 3 locale tests fail:

vstinner@WIN C:\vstinner\python\3.8>python -m test -v test_locale test__locale

======================================================================
ERROR: test_getsetlocale_issue1813 (test.test_locale.TestMiscellaneous)
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Traceback (most recent call last):
  File "C:\vstinner\python\3.8\lib\test\test_locale.py", line 567, in test_getsetlocale_issue1813
    locale.setlocale(locale.LC_CTYPE, loc)
  File "C:\vstinner\python\3.8\lib\locale.py", line 608, in setlocale
    return _setlocale(category, locale)
locale.Error: unsupported locale setting

======================================================================
ERROR: test_float_parsing (test.test__locale._LocaleTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\vstinner\python\3.8\lib\test\test__locale.py", line 184, in test_float_parsing
    if localeconv()['decimal_point'] != '.':
UnicodeDecodeError: 'locale' codec can't decode byte 0xa0 in position 0: decoding error

======================================================================
ERROR: test_lc_numeric_localeconv (test.test__locale._LocaleTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\vstinner\python\3.8\lib\test\test__locale.py", line 130, in test_lc_numeric_localeconv
    formatting = localeconv()
UnicodeDecodeError: 'locale' codec can't decode byte 0xa0 in position 0: decoding error

test_float_parsing() fails for locales:

* "ka_GE"
* "fr_FR.UTF-8"

test_lc_numeric_localeconv() fails for locales:

* 'ka_GE'
* 'fr_FR.UTF-8'
* 'ps_AF'

test_getsetlocale_issue1813() fails with:

   testing with ('tr_TR', 'ISO8859-9')

Example:

vstinner@WIN C:\vstinner\python\3.8>python
Running Release|x64 interpreter...
Python 3.8.0b4+ (heads/pr/16490:8a204fd07c, Sep 30 2019, 14:29:53) [MSC v.1916 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.

>>> import locale
>>> locale.setlocale(locale.LC_CTYPE, 'tr_TR')
'tr_TR'
>>> loc=locale.getlocale(locale.LC_CTYPE)  
>>> loc
('tr_TR', 'ISO8859-9')
>>> locale.setlocale(locale.LC_CTYPE, loc) 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\vstinner\python\3.8\lib\locale.py", line 608, in setlocale
    return _setlocale(category, locale)
locale.Error: unsupported locale setting

# It works using the low-level _locale module
# which doesn't parse setlocale() output

>>> import _locale                        
>>> _locale.setlocale(_locale.LC_CTYPE, None) 
'tr_TR'
>>> locale.setlocale(locale.LC_CTYPE, "tr_TR") 
'tr_TR'