diff --git a/mercurial/i18n.py b/mercurial/i18n.py
--- a/mercurial/i18n.py
+++ b/mercurial/i18n.py
@@ -23,7 +23,6 @@
     from typing import (
         Callable,
         List,
-        Optional,
     )
 
 
@@ -71,7 +70,7 @@
 
 
 def gettext(message):
-    # type: (Optional[bytes]) -> Optional[bytes]
+    # type: (bytes) -> bytes
     """Translate message.
 
     The message is looked up in the catalog to get a Unicode string,