Edit error message for Username on registration

common/djangoapps/student/forms.py

@@ -120,7 +120,8 @@ class AccountCreationForm(forms.Form):
         max_length=30,
         error_messages={
             "required": _USERNAME_TOO_SHORT_MSG,
-            "invalid": _("Usernames must contain only letters, numbers, underscores (_), and hyphens (-)."),
+            "invalid": _("Usernames can only contain Roman letters, western numerals (0-9), underscores (_), and "
+                         "hyphens (-)."),
             "min_length": _USERNAME_TOO_SHORT_MSG,
             "max_length": _("Username cannot be more than %(limit_value)s characters long"),
         }

common/djangoapps/student/tests/test_create_account.py

@@ -471,7 +471,8 @@ class TestCreateAccountValidation(TestCase):
 
         # Invalid
         params["username"] = "invalid username"
-        assert_username_error("Usernames must contain only letters, numbers, underscores (_), and hyphens (-).")
+        assert_username_error("Usernames can only contain Roman letters, western numerals (0-9), underscores (_), and "
+                              "hyphens (-).")
 
     def test_email(self):
         params = dict(self.minimal_params)