diff --git a/wp-includes/wp-l10n.php b/wp-includes/wp-l10n.php
index 63c97d9b63..1ddceb5056 100644
--- a/wp-includes/wp-l10n.php
+++ b/wp-includes/wp-l10n.php
@@ -14,6 +14,8 @@ if (empty($locale)) {
     $locale = 'en_US';
 }
 
+$locale = apply_filters('locale', $locale);
+
 require_once(ABSPATH . 'wp-includes/streams.php');
 require_once(ABSPATH . 'wp-includes/gettext.php');