Role/Capability: Introduce capabilities dedicated to installing and updating language files.

The new meta capabilities are called `install_languages` and `update_languages`. Prior to this change, there were no proper capability checks applied. Instead only the filesystem and related constants were checked, and for actual permissions a rather vague fallback was used where a user needed to have at least one of the other updating capabilities. In addition to being generally more verbose, the new capabilities make it possible for example to allow a user to update languages, but nothing else. By default they fall back to the original way of how they were handled.

Props johnbillion, flixos90.
Fixes #39677.


git-svn-id: https://develop.svn.wordpress.org/trunk@41268 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/options-general.php

@@ -151,7 +151,7 @@ if ( ! empty( $languages ) || ! empty( $translations ) ) {
 				'selected'     => $locale,
 				'languages'    => $languages,
 				'translations' => $translations,
-				'show_available_translations' => ( ! is_multisite() || is_super_admin() ) && wp_can_install_language_pack(),
+				'show_available_translations' => current_user_can( 'install_languages' ),
 			) );
 
 			// Add note about deprecated WPLANG constant.