diff --git a/src/calibre/utils/localization.py b/src/calibre/utils/localization.py
index e60a3233c6..94f3923acf 100644
--- a/src/calibre/utils/localization.py
+++ b/src/calibre/utils/localization.py
@@ -42,6 +42,8 @@ def get_lang():
             lang = match.group()
     if lang == 'zh':
         lang = 'zh_CN'
+    if lang is None:
+        lang = 'en'
     return lang
 
 def messages_path(lang):