diff --git a/mercurial/i18n.py b/mercurial/i18n.py
--- a/mercurial/i18n.py
+++ b/mercurial/i18n.py
@@ -36,9 +36,12 @@ def gettext(message):
     if message is None:
         return message
 
-    # We cannot just run the text through encoding.tolocal since that
-    # leads to infinite recursion when encoding._encoding is invalid.
     try:
+        # encoding.tolocal cannot be used since it will first try to
+        # decode the Unicode string. Calling u.decode(enc) really
+        # means u.encode(sys.getdefaultencoding()).decode(enc). Since
+        # the Python encoding defaults to 'ascii', this fails if the
+        # translated string use non-ASCII characters.
         u = t.ugettext(message)
         return u.encode(encoding.encoding, "replace")
     except LookupError: