On my Windows, some non-ASCII characters cause this warning:
d:\dev\cpython\modules\expat\xmltok.c : warning C4819:
The file contains a character that cannot be represented in
the current code page (936). Save the file in Unicode format
to prevent data loss.
This patch fixes the warnings, it's applicable to master/3.8 branches.
https://github.com/animalize/cpython/commit/daced7575ec70ef1f888c6854760e230cda5ea64
Maybe this trivial problem is not worth a new commit, it can be fixed along with other warnings.