Extract of an interesting message (msg111432) of #8775 (issue specific to Mac OS X):

<< A system where the filesystem encoding doesn't match the locale encoding is hard to get right. While it would be possible to add sys.cmdlineencoding that doesn't actually solve the semantic problem because external tools might not cooperate.

That is, most system tools seem to work with bytes internally and do not treat arguments as text encoded in the locale encoding that should be re-encoded in the filesystem encoding before passing them to the C APIs.

That is, when calling "ls somefile" the "ls" command will pass the bytes in argv[1] to the POSIX routines for getting file information without trying to reencode. >>