I introduced initfsencoding() in #8610 to ensure that Py_FileSystemEncoding is not more NULL. In the discussion, Marc Lemburg noticed that falling back the UTF-8 on nl_langinfo(CODESET) error is a bad idea: ASCII is better (I agree).
We cannot fall back to ASCII yet because there are two other problems that have to be fixed before that:
- Python3 doesn't support surrogates in module filenames: see #8611
- If Py_FileSystemEncoding is NULL, encoding functions fallback to utf-8 (PyUnicode_GetDefaultEncoding()). #8715 proposes a new PyUnicode_EncodeFSDefault() function to fix this problem
Attached patch is a partial fix for this issue.