As the AIX complaint is (was once the PR merges):
AssertionError: "['h\\xc3\\xa9\\xe2\\x82\\xac']" != "['h\\udcc3\\udca9\\udce2\\udc82\\udcac']"
- ['h\xc3\xa9\xe2\x82\xac']
+ ['h\udcc3\udca9\udce2\udc82\udcac']

And the HP-UX complaint is:
  File "/var/osipovmi/cpython/Lib/test/test_utf8_mode.py", line 223, in check
    self.assertEqual(args, ascii(expected), out)
AssertionError: "['h\\xc3\\xa9\\xe2\\x82\\xac']" != "['h\\udcc3\\udca9\\udce2\\udc82\\udcac']"
- ['h\xc3\xa9\xe2\x82\xac']
+ ['h\udcc3\udca9\udce2\udc82\udcac']

Maybe a change such as:

--- a/Lib/test/test_utf8_mode.py
+++ b/Lib/test/test_utf8_mode.py
@@ -219,6 +219,8 @@ class UTF8ModeTests(unittest.TestCase):
         check('utf8', [arg_utf8])
         if sys.platform == 'darwin' or support.is_android:
             c_arg = arg_utf8
+        elif (platform.system == "AIX") or
+              sys.platform.startswith("hp-ux"):
+            c_arg = arg.decode('iso-8859-1')
         else:
             c_arg = arg_ascii
         check('utf8=0', [c_arg], LC_ALL='C')

I mention this because it seems neither roman8 nor roman9 have 'official' iso names or alias (correct me if I am wrong).