Recommend setting up more locales

[serhiy-storchaka]

Some tests require specific locales. Often non-default non-English non-UTF-8 locales. If such locale is not available the test is skip or ran in the dry-run mode. It would be nice to add a recommendation to set up additional locales on buildbots and on developer's machines.

Recommended locales:

• en_US (en_US.utf8, en_US.iso88591) -- the standard
• de_DE (de_DE.UTF-8) or fr_FR (fr_FR.utf8, fr_FR.iso88591, fr_FR.iso885915@euro) -- common non-English locales
• tr_TR (tr_TR.iso88599) -- Turkish has peculiar rules for upper/lower cases of "i" and "I".
• ps_AF -- used in test_decimal

See also https://github.com/python/cpython/issues/67660.