Tests use following locales:

test_types: en_US.UTF-8
test_codecs: tr_TR
test_decimal: ps_AF
test_float: fr_FR or de_DE
test_imaplib: de_DE or fr_FR
test_locale: (en_US.UTF-8, en_US.ISO-8859-1, en_US.US-ASCII, or en_US), tr_TR
test_pickle: de_DE or fr_FR
test_re: en_US.ISO-8859-1, en_US.UTF-8
test_strptime: en_US.UTF-8, de_DE.UTF-8
test_time: fr_FR
test_unicode: de_DE or fr_FR

And test__locale uses locales from the long list.

So it would be good to setup following locales on all buildbots:

en_US, en_US.UTF-8, en_US.ISO-8859-1, en_US.ISO-8859-1, en_US.US-ASCII, de_DE, de_DE.UTF-8, fr_FR, tr_TR, ps_AF