> manpage for nl_langinfo() doesn't mention any errors that could
> be raised by it

It's more about get_codeset(). This function can fail for different reasons:

 - nl_langinfo() result is an empty string: "If item is not valid, a pointer to an empty string is returned." say the manpage
 - _PyCodec_Lookup() failed: unable to import the encoding codec module, there is no such codec, codec machinery is broken, etc.
 - the codec has no "name "attribute
 - strdup() failure (no more memory)

Do you think that you should fallback to ASCII if nl_langinfo() result is an empty string, and UTF-8 otherwise? get_codeset() failure is very unlikely, and I think that fallback to UTF-8 is just fine. A warning is printed to stderr, the user should try to understand why get_codeset() failed.

You can at least reproduce the _PyCodec_Lookup() error with #8611.

My problem is also that the file system encoding is required (encoding != None) by os.environ mapping with my os.environb patch. (#8603)