Index: src/wp-includes/general-template.php
===================================================================
--- src/wp-includes/general-template.php	(revision 36768)
+++ src/wp-includes/general-template.php	(working copy)
@@ -709,7 +709,8 @@
 			break;
 		case 'language':
 			$output = get_locale();
-			$output = str_replace('_', '-', $output);
+			$output = str_replace( '_', '-', $output );
+			$output = str_replace( '-formal', '', $output );
 			break;
 		case 'text_direction':
 			_deprecated_argument( __FUNCTION__, '2.2', sprintf(