If the fullpath to the python3 binary contains a non-ASCII character and the file system encoding is ASCII, Python fails with:
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Could not find platform independent libraries <prefix>
Could not find platform dependent libraries <exec_prefix>
Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]
Fatal Python error: Py_Initialize: can't initialize sys standard streams
ImportError: No module named encodings.utf_8
Abandon
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The file system encoding is set to ASCII if there is no locale (eg. LANG=C).

The problem is that the command line argument, especially argv[0], is stored to a wchar_t* string using surrogates to store undecodable bytes.

Attached patch fixes calculate_path() and import functions to support surrogates. Details:

 * Initialize Py_FileSystemDefaultEncoding earlier in Py_InitializeEx(), because its value is required to encode unicode using surrogates to bytes
 * Rename char2wchar() to _Py_char2wchar(), the function is not more static ; and create function _Py_wchar2char()
 * Escape surrogates (reimplement surrogateescape decoder) in calculate_path() subfunctions (_wstat, _wgetcwd, _Py_wreadlink)
 * Use surrogateescape error handler in find_module(), NullImporter_init() and zipimporter_init()
 * Write a "fastpath" (I don't know the right term: is it an hack?) for utf-8 encoding with surrogateescape error handler in PyUnicode_AsEncodedObject() and PyUnicode_AsEncodedString(): required because these functions are called by codecs module is initialized

The patch is a work in progress: there are some FIXME (I don't know if the string should be encoded/decoded using surrogates or not).

I only tested ASCII and UTF-8 file system encodings. I don't know if we can support more encodings. Python has few builtin encodings. Other encodings are implemented in Python: we have to import them, but we need the codec to import a module, so...

I don't think that Windows is affected by this issue because it has a better API for unicode filenames and command line arguments, and most patched functions are surrounded by #ifndef WINDOWS ... #endif