The only locale that doesn't include language information is the UTF-8 one, there is no locale named "US-ASCII".
See /usr/share/locale on an OSX system.
PS. The more I look at locale.py the more problems I find with it. The code makes a unwarranted assumptions about locales that aren't actually true on all systems.
For example:
>>> locale.normalize('ja_JP')
'ja_JP.eucJP'
That's not true on OSX, /usr/share/locale/ja_JP/LC_CTYPE is a symlink to /usr/share/locale/UTF-8/LC_CTYPE.
AFAIK *all* locale's on OSX use UTF-8.