Index: Lib/locale.py
===================================================================
--- Lib/locale.py	(Revision 74327)
+++ Lib/locale.py	(Arbeitskopie)
@@ -207,8 +207,12 @@
     """Formats a string in the same way that the % formatting would use,
     but takes the current locale into account.
     Grouping is applied if the third parameter is true."""
-    percents = list(_percent_re.finditer(f))
-    new_f = _percent_re.sub('%s', f)
+    # filter for %%
+    percents = [perc for perc in _percent_re.finditer(f) \
+        if perc.group()[-1] != '%']
+    new_f = f
+    for perc in percents[::-1]:
+        new_f = new_f[:perc.start()] + '%s' + new_f[perc.end():]
 
     if isinstance(val, tuple):
         new_val = list(val)