For the record, this can be now reproduced under Linux by forcing different locale and filesystem encodings:

$ PYTHONFSENCODING=utf8 LANG=ISO-8859-1 ./python -m test.regrtest test_cmd_line

[1/1] test_cmd_line
test test_cmd_line failed -- Traceback (most recent call last):
  File "/home/antoine/py3k/__svn__/Lib/test/test_cmd_line.py", line 109, in test_run_code
    assert_python_ok('-c', command)
  File "/home/antoine/py3k/__svn__/Lib/test/script_helper.py", line 35, in assert_python_ok
    return _assert_python(True, *args)
  File "/home/antoine/py3k/__svn__/Lib/test/script_helper.py", line 31, in _assert_python
    "stderr follows:\n%s" % (rc, err.decode('ascii', 'ignore')))
AssertionError: Process return code is 1, stderr follows:
Traceback (most recent call last):
  File "<string>", line 1, in <module>
TypeError: ord() expected a character, but string of length 2 found