Role/Capability: Prevent a fatal error when checking a language capability early or in the frontend.

The meta capabilities `install_languages` and `update_languages` rely on the admin function `wp_can_install_language_pack()`. That function in turn relies on `request_filesystem_credentials()`, so it needs to be ensured that this function is available as well.

Fixes #42230.


git-svn-id: https://develop.svn.wordpress.org/trunk@41885 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/capabilities.php

@@ -432,6 +432,10 @@ function map_meta_cap( $cap, $user_id ) {
 		break;
 	case 'install_languages':
 	case 'update_languages':
+		if ( ! function_exists( 'request_filesystem_credentials' ) ) {
+			require_once( ABSPATH . 'wp-admin/includes/file.php' );
+		}
+
 		if ( ! function_exists( 'wp_can_install_language_pack' ) ) {
 			require_once( ABSPATH . 'wp-admin/includes/translation-install.php' );
 		}