Windows desktop skus have a default ANSI codepage (returned by GetACP()) of 1252 (Western European).  Windows IoT Core and Windows Nano Server have a default codepage of 65001 (UTF-8). 

This causes test_site.StartupImportTests.test_startup_imports to fail on Windows IoT Core and Windows Nano Server because cp65001.py is loaded instead of the frozen cp1252.py at startup.

I tried changing the default codepage to 65001 on my dev machine and rebuilding Python and it had no effect that I could tell on the generated frozen importlibs.

The simplest solutions would be for the test_startup_imports test to be skipped or changed to pass when the locale.getpreferredencoding() returns 'cp65001'