This uses the new strings for alt text and site icon description that were introduced in [57713] as a part of #54370.
The strings are translated in PHP and then use `wp.i18n.sprintf` since the alt text strings live in a PHP file even though they are output as part of a template that is used in JavaScript.
Props westonruter, swissspidy, jorbin.
Fixes#60641.
Built from https://develop.svn.wordpress.org/trunk@57730
git-svn-id: http://core.svn.wordpress.org/trunk@57231 1a063a9b-81f0-0310-95a4-ce76da25c4cd