Pretty easy to overlook in the grand scheme of things.
Might want to let them know that they'll need to duplicate the msvc(p|r) runtime files (both the 100 and the 120) in the Sigil\python3 directory, as well. Profiling with Dependency Walker while running the test plugin reveals that Python ctypes access to the hunspell.dll looks to the Windows\System folder for the runtimes if they're not adjacent to the Python interpreter/dll.
If they get it going, I may just leave them to it. As to the file-paths with non-ansi characters ... that may be a non-starter. The python interpreter can't seem to cope with a file-path that has non-ansi characters in the "home" entry of the pyvenv.cfg file (at least on Windows). Can't win 'em all I guess.