Ticket #42574: 42574.2.diff

src/wp-includes/l10n.php

@@ -1210 +1210 @@
                 selected( '', $parsed_args['selected'], false )
         );
 
-        // List installed languages. 
+        // List installed languages.
         foreach ( $languages as $language ) {
                 $structure[] = sprintf(
                         '<option value="%s" lang="%s"%s data-installed="1">%s</option>',
@@ -1332 +1332 @@
 
         return $wp_locale_switcher->is_switched();
 }
+
+/**
+ * Parses a WordPress locale identifier into an ISO 639 locale identifier.
+ *
+ * @since 5.0.0
+ *
+ * @param string $locale A WordPress locale.
+ * @return string Parsed ISO locale.
+ */
+function wp_parse_iso_locale( $locale ) {
+        $locale = str_replace( '_', '-', $locale );
+
+        if ( substr_count( $locale, '-' ) > 1 ) {
+                $locale = implode( '-', array_slice( explode( '-', $locale ), 0, 2 ) );
+        }
+
+        return $locale;
+}

src/wp-includes/script-loader.php

@@ -357 +357 @@
         $scripts->add( 'mediaelement-migrate', "/wp-includes/js/mediaelement/mediaelement-migrate$suffix.js", array(), false, 1);
 
         did_action( 'init' ) && $scripts->add_inline_script( 'mediaelement-core', sprintf( 'var mejsL10n = %s;', wp_json_encode( array(
-                'language' => strtolower( str_replace( '_', '-', is_admin() ? get_user_locale() : get_locale() ) ),
+                'language' => strtolower( wp_parse_iso_locale( is_admin() ? get_user_locale() : get_locale() ) ),
                 'strings'  => array(
                         'mejs.install-flash'       => __( 'You are using a browser that does not have Flash player enabled or installed. Please turn on your Flash player plugin or download the latest version from https://get.adobe.com/flashplayer/' ),
                         'mejs.fullscreen-off'      => __( 'Turn off Fullscreen' ),