> mbstowcs uses LC_CTYPE. Is that correct and consistent with the way
> default encoding under UNIX is handled by Py3k?

It's correct, but it's not consistent with the default encoding - there
isn't really any default encoding in Py3k. More specifically,
PyUnicode_FromString uses UTF-8, but not as a (changeable) default,
but as part of its API specification.
Command line arguments are in the locale's charset, so the LC_CTYPE
must be used to convert them.

> Would a Py_MainW or similar wrapper be easier on the UNIX guys? I'm just
> asking, I don't have a definite idea.

See above. The current POSIX implementation is incorrect also. It should
use the locale's encoding, but doesn't.