On Mac OS X, the XCode libc already ignores the locale settings and just uses UTF-8 as the default text encoding, so the hardcoding in CPython aligns with that behaviour.

That isn't the case on other *nix systems - there, we need CPython to be consistent with the configured C/C++ locale, *and* we need it to be using something other than ASCII as the default encoding.

Answer: coerce the default locale from C to C.UTF-8 (if available), or to en_US.UTF-8 (for older distros that don't provide C.UTF-8). (The latter aspect isn't in the PEP yet, it's an improvement that came up in the linux-sig discussions: https://github.com/python/peps/issues/171 )