diff --git a/src/i18n.py b/src/i18n.py
index 0831ab80c..eb7150bd1 100644
--- a/src/i18n.py
+++ b/src/i18n.py
@@ -353,7 +353,7 @@ class InternationalizedFunction:
 class InternationalizedString(str):
     """Simple subclass to str, that allow to add attributes. Also used to
     know if a string is already localized"""
-    pass
+    __slots__ = ('_original', '_internationalizer')
 
 def internationalizeDocstring(obj):
     """Decorates functions and internationalize their docstring.