bug#81606: Mojibake with UTF-8 file names

> Date: Sun, 16 Aug 2026 14:29:54 +0000
> Cc: [email protected], [email protected]
> From: Werner LEMBERG <[email protected]>
> 
> >> If a master file `foo` is specified in the local variables block,
> >> AUCTeX checks whether it is exists, otherwise it gets created.
> >> This string `foo` must be given in the encoding specified by the
> >> `coding` cookie.
> > 
> > But this is trivially correct: any non-ASCII text in a file which has
> > a 'coding:' cookie _must_ be encoded in the encoding specified by
> > 'coding:".  Right?
> 
> There might be situations where the file encoding and the file name
> encoding differ, for example on Windows.

No, if the file name is specified by the same file that has the
'coding:' cookie, that cannot happen.

> I don't know enough about the encoding handling in Emacs whether it
> automatically maps UTF-8 encoded file name strings (as implied by
> the `coding` cookie) to UTF-16...

Of course it does.  How else could Emacs support arbitrary non-ASCII
characters in file names on Windows?

> > If you want to require the 'coding:' cookie in all cases, that's
> > fine, but then latexenc.el is not needed at all, see above.
> 
> Well, the AUCTeX documentation doesn't require it yet — otherwise I
> wouldn't have noticed the problem.  I think it's a good thing if Emacs
> has a heuristic fallback mechanism to handle the case without a
> `coding` cookie.

And for that case I think the recommendation should be to encode the
file name in UTF-8.