PEP 538 [1] coerces the C locale to UTF-8 by setting the locale environment variables (LC_ALL, LANG). The PEP has an implementation at issue 28180 as pep538_coerce_legacy_c_locale_v3.diff, and the patch fixes test_nonascii when run on the Android emulators (api 21 and 24). This is as expected as now both Python and Readline are in agreement and use the same encoding.
I think we should wait for the resolution of PEP 538 and of issue 28684. If this does not happen, I agree we should skip the test with the message you are proposing Martin.
[1] https://www.python.org/dev/peps/pep-0538