bug#81606: Mojibake with UTF-8 file names

> From: Arash Esbati <[email protected]>
> Cc: Werner LEMBERG <[email protected]>,  [email protected]
> Date: Sun, 16 Aug 2026 21:35:05 +0200
> 
> Eli Zaretskii <[email protected]> writes:
> 
> > I thought I already did, but here it is again:
> >
> >   If you're using non-ASCII characters in the name of the master file,
> >   you should give Emacs a hint about the correct coding of the current
> >   file like this:
> >   
> >   @example
> >   %%% Local Variables:
> >   %%% coding: utf-8
> >   %%% TeX-master: "ä-master"
> >   %%% End:
> >   @end example
> >
> >   In general, we recommend to use UTF-8 for any non-ASCII text.
> 
> Thanks Eli, I will install your suggestion.  Do you want to add
> something similar to Emacs manual as well?  The issue is not specific to
> AUCTeX and its `TeX-master'.

I can add it to "TeX Print", where the tex-main-file variable is
documented.  Is that okay?

And I still don't think we have a consensus regarding the fix for
latexenc.el: do we want to decode using UTF-8 or 'undecided'?