bug#59715: 28.2; Emacs crashes after ``turkish-case-conversion-enable''

[Eli Zaretskii]

> Cc: 59715@debbugs.gnu.org
> Date: Sun, 04 Dec 2022 14:09:46 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> 
> Thanks.  I think I know what happens.  It's the problem with down-casing
> Iosevka in your locale, which produces "ıosevka", with the first letter
> being dotless i.  And that down-cased name doesn't match anything.
> 
> Hmm...

One way to work around this tricky issue is to specify the font in all
lower-case characters to begin with.

How do you tell Emacs to use Iosevka as the default font?