bug#21387: 24.3; ediff bug with french

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Thu, 27 May 2021 00:38:56 +0200
> Cc: 21387@debbugs.gnu.org
> 
> Lars Ingebrigtsen <larsi@gnus.org> writes:
> 
> > Any comments?  Is this the best way to do this sort of stuff?  The
> > LOCALE/LANGUAGE/LC_* variables can be kinda confusing.
> 
> There were no comments, so I've now pushed this change.

FTR, please note that this fix is 100% reliable only on Posix systems.
MS-Windows's setlocale doesn't heed the LC_* environment variables,
unless the program was built with the Gnulib replacement for
setlocale, or took special care to access the environment from the
application code.  Some programs do, others don't, so don't expect
this to work for every port of Diff out there.