Ah, you're right - I missed that the ForceASCII stuff was on the non-Windows side of an ifdef so it's literally impossible for that change to affect Windows, not just highly unlikely.

It would be interesting to compare the output of `python -vv` between the working case and the non-working case, as the second level of verbosity will print out all the different candidates the two versions are considering, and which ones they're accepting. For example, here's my Linux system Python up to the point where it finishes importing the UTF-8 codec:

========================
$ python3 -vv
import _frozen_importlib # frozen
import _imp # builtin
import '_thread' # <class '_frozen_importlib.BuiltinImporter'>
import '_warnings' # <class '_frozen_importlib.BuiltinImporter'>
import '_weakref' # <class '_frozen_importlib.BuiltinImporter'>
# installing zipimport hook
import 'zipimport' # <class '_frozen_importlib.BuiltinImporter'>
# installed zipimport hook
import '_frozen_importlib_external' # <class '_frozen_importlib.FrozenImporter'>
import '_io' # <class '_frozen_importlib.BuiltinImporter'>
import 'marshal' # <class '_frozen_importlib.BuiltinImporter'>
import 'posix' # <class '_frozen_importlib.BuiltinImporter'>
import _thread # previously loaded ('_thread')
import '_thread' # <class '_frozen_importlib.BuiltinImporter'>
import _weakref # previously loaded ('_weakref')
import '_weakref' # <class '_frozen_importlib.BuiltinImporter'>
# /usr/lib64/python3.7/encodings/__pycache__/__init__.cpython-37.pyc matches /usr/lib64/python3.7/encodings/__init__.py
# code object from '/usr/lib64/python3.7/encodings/__pycache__/__init__.cpython-37.pyc'
# trying /usr/lib64/python3.7/codecs.cpython-37m-x86_64-linux-gnu.so
# trying /usr/lib64/python3.7/codecs.abi3.so
# trying /usr/lib64/python3.7/codecs.so
# trying /usr/lib64/python3.7/codecs.py
# /usr/lib64/python3.7/__pycache__/codecs.cpython-37.pyc matches /usr/lib64/python3.7/codecs.py
# code object from '/usr/lib64/python3.7/__pycache__/codecs.cpython-37.pyc'
import '_codecs' # <class '_frozen_importlib.BuiltinImporter'>
import 'codecs' # <_frozen_importlib_external.SourceFileLoader object at 0x7f0ea616eb70>
# trying /usr/lib64/python3.7/encodings/aliases.cpython-37m-x86_64-linux-gnu.so
# trying /usr/lib64/python3.7/encodings/aliases.abi3.so
# trying /usr/lib64/python3.7/encodings/aliases.so
# trying /usr/lib64/python3.7/encodings/aliases.py
# /usr/lib64/python3.7/encodings/__pycache__/aliases.cpython-37.pyc matches /usr/lib64/python3.7/encodings/aliases.py
# code object from '/usr/lib64/python3.7/encodings/__pycache__/aliases.cpython-37.pyc'
import 'encodings.aliases' # <_frozen_importlib_external.SourceFileLoader object at 0x7f0ea6183550>
import 'encodings' # <_frozen_importlib_external.SourceFileLoader object at 0x7f0ea616e5c0>
# trying /usr/lib64/python3.7/encodings/utf_8.cpython-37m-x86_64-linux-gnu.so
# trying /usr/lib64/python3.7/encodings/utf_8.abi3.so
# trying /usr/lib64/python3.7/encodings/utf_8.so
# trying /usr/lib64/python3.7/encodings/utf_8.py
# /usr/lib64/python3.7/encodings/__pycache__/utf_8.cpython-37.pyc matches /usr/lib64/python3.7/encodings/utf_8.py
# code object from '/usr/lib64/python3.7/encodings/__pycache__/utf_8.cpython-37.pyc'
import 'encodings.utf_8' # <_frozen_importlib_external.SourceFileLoader object at 0x7f0ea6191278>
========================