Ticket #38798: 38798.patch

src/wp-admin/includes/user.php

@@ -100 +100 @@
                         $locale = sanitize_text_field( $_POST['locale'] );
                         if ( 'site-default' === $locale ) {
                                 $locale = '';
+                        } elseif ( '' === $locale ) {
+                                $locale = 'en_US';
                         } elseif ( ! in_array( $locale, get_available_languages(), true ) ) {
-                                $locale = 'en_US';
+                                $locale = '';
                         }
 
                         $user->locale = $locale;