bug#50752: 28.0.50; easy-menu-define lowers the menu-bar key

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: stefan@marxist.se,  shuguang79@qq.com,  50752@debbugs.gnu.org
> Date: Tue, 19 Oct 2021 14:07:59 +0200
> 
> Second of all -- to handle this specific, very unusual case (i.e.,
> downcasing a ascii character gets us a non-ascii character), when we
> detect this issue, we should just abort this loop and call
> do_casify_multibyte_string instead.

You mean, you want to special-case Turkish (and a couple of similar)
locale?  That might be possible, but the more general problem will
still be left more or less intact.  And then we need to consider how
many places don't expect to get multibyte string when they downcase a
unibyte one.