bug#15803: default-file-name-coding-system: utf-8 better than latin-1 these days?

[Glenn Morris <rgm@gnu.org>]

Glenn Morris wrote:

>> mule-cmds.el calls reset-language-environment, and language/english.el
>> calls set-language-info-alist; both have the effect of resetting
>> default-file-name-coding-system to latin-1 (!? an interesting
>> "default" for a Unicode-era Emacs, perhaps Handa-san could comment why
>> we still do that).
>
> I know nothing about this, but eg glib defaults to utf-8, which seems
> like a better default to me these days:
>
> https://developer.gnome.org/glib/stable/glib-Character-Set-Conversion.html#file-name-encodings

... 4 years pass and latin-1 fails to make a comeback.

For some reason, I thought it was difficult to change the default to
utf-8 due to bootstrap ordering issues. This was probably prompted by
this comment in reset-language-environment:

  ;; On Darwin systems, this should be utf-8-unix, but when this file is loaded
  ;; that is not yet defined, so we set it in set-locale-environment instead.
  (setq default-file-name-coding-system 'iso-latin-1-unix)

But looking at it now, I cannot see what this comment is referring to.

If I change reset-language-environment so that it sets
default-file-name-coding-system (and default-sendmail-coding-system)
to 'utf-8, then a bootstrap works fine.

It looks like this stuff was all rewritten in Emacs 23.
Before that, there used to be international/utf-8.el,
which was indeed loaded after mule-cmds.
But since Emacs 23, mule-conf seems to define everything.
(But that rewrite seems to predate the above comment about Darwin...?)

So should the default finally be changed to utf-8?