After doing some research on this myself, it looks like it's case-sensitive for case-sensitive filesystems and not case-sensitive for filesystems that aren't. You can verify by inspecting how Babel determines whether a locale exists or not, and how it loads the locale data files:
By the way, I think CLDR's spec says that locale identifiers should NOT be case sensitive (http://cldr.unicode.org/core-spec – search for "case-insensitive" – "All identifier field values are case-insensitive.") so if that's indeed true I think it'd be nice if Babel could normalize this somehow to support case-insensitivity independent of the filesystem.
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jeremydw commented on Jul 28, 2015
After doing some research on this myself, it looks like it's case-sensitive for case-sensitive filesystems and not case-sensitive for filesystems that aren't. You can verify by inspecting how Babel determines whether a locale exists or not, and how it loads the locale data files:
https://github.com/mitsuhiko/babel/blob/master/babel/localedata.py#L35
jeremydw commented on Jul 28, 2015
By the way, I think CLDR's spec says that locale identifiers should NOT be case sensitive (http://cldr.unicode.org/core-spec – search for "case-insensitive" – "All identifier field values are case-insensitive.") so if that's indeed true I think it'd be nice if Babel could normalize this somehow to support case-insensitivity independent of the filesystem.
akx commented on Jan 14, 2016
#309 will fix this in the sense that it will become impossible to create a en_us locale (should be en_US).
akx commented on Jan 25, 2022
#814 is related to this case (in)sensitivity.