bug#51733: 27.1; Detect impossible email addresses better

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: Eli Zaretskii <eliz@gnu.org>,  51733@debbugs.gnu.org
> Date: Wed, 19 Jan 2022 14:46:42 +0100
> 
> Robert Pluim <rpluim@gmail.com> writes:
> 
> > How about "Contains suspicious characters or mix of characters"? That
> > would at least point users in the right direction.
> 
> I'm not 100% that it's not misleading in all cases, though.  textsec
> still doesn't implement "Unicode Identifier and Pattern Syntax":
> 
>   https://www.unicode.org/reports/tr31/
> 
> There's some other stuff in there...  But I might be quibbling.

My suggestion for the diagnostic in this case is:

  %s mixes characters from different scripts in suspicious ways