bug#49982: 27.2; ispell.el fails to find a Hunspell dictionary to use as default despite ispell-dictionary being set

[Kisaragi Hiu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

 > Indeed, defining DICTIONARY in the environment is the way to control
the default dictionary.  It is documented in the Hunspell's man page.
Why cannot it be the solution for when no Hunspell dictionary could be
found that matches the locale?  Using $DICTIONARY should solve your
problem both inside Emacs and outside it.

I don't know, maybe I'm biased here. Hunspell has its quirks, but isn't 
it ispell.el's job to work around quirks in spellcheckers, and not the 
end user's? ispell.el worked around Hunspell 1.7's new output quirk. Why 
can't it work around this quirk?

*My* problem is already solved by using the workaround. The bug is that 
nobody should have to use the workaround.

Using environment variables to configure subprocesses is always 
something that a user can do, but, as you know, there's a reason why 
ispell.el exposes spellchecker options through Emacs user options.

Besides, which dictionary one specifies in `DICTIONARY` doesn't actually 
matter, it just needs to be one that exists, as it will be overridden by 
ispell-dictionary when ispell.el actually starts spellchecking. You can 
do (in emacs -Q):

     (setenv "LANG" "ja_JP") ; trigger the quirk
     (setenv "DICTIONARY" "en_US") ; tame ispell-find-hunspell-dictionaries
     (setq ispell-program (executable-find "hunspell")
           ispell-dictionary "en_GB")
     (flyspell-mode)

and see that it's spellchecking color to colour. (Try typing "color" 
then running M-x flyspell-auto-correct-previous-word)

---

ispell-dictionary is ispell.el's way of specifying the main dictionary. 
The manual:

 > Spell-checkers look up spelling in two dictionaries: the standard
dictionary and your personal dictionary.  The standard dictionary is
specified by the variable ‘ispell-local-dictionary’ or, if that is
‘nil’, by the variable ‘ispell-dictionary’.  If both are ‘nil’, the
spelling program’s default dictionary is used.

The spelling program's default should only ever have an effect when both 
ispell-local-dictionary and ispell-dictionary is nil.