- Launchpad #151020: HTTP_CHAR_SET headers containing 'x-user-defined'
        caused a LookupError exception. Unknown encodings are from now on
        silently discarded.

doc/CHANGES.txt

@@ -175,6 +175,10 @@ Zope Changes
 
     Bugs Fixed
 
+      - Launchpad #151020: HTTP_CHAR_SET headers containing 'x-user-defined'
+        caused a LookupError exception. Unknown encodings are from now on
+        silently discarded.
+
       - Launchpad #143902: Fixed App.ImageFile to use a stream iterator to
         output the file. Avoid loading the file content when guessing the
         mimetype and only load the first 1024 bytes of the file when it cannot

lib/python/Products/PageTemplates/tests/testZopePageTemplate.py

@@ -131,6 +131,15 @@ class ZPTUnicodeEncodingConflictResolution(ZopeTestCase):
         result = zpt.pt_render()
         self.assertEqual(result.startswith(unicode('<div></div>', 'iso-8859-15')), True)
 
+    def testBug151020(self):
+        manage_addPageTemplate(self.app, 'test', 
+                               text='<div tal:content="structure python: %s" />' % "''",
+                               encoding='iso-8859-15')
+        zpt = self.app['test']
+        self.app.REQUEST.set('HTTP_ACCEPT_CHARSET', 'x-user-defined, iso-8859-15,utf-8')
+        self.app.REQUEST.set('data', unicode('', 'iso-8859-15').encode('utf-8'))
+        result = zpt.pt_render()
+        self.assertEqual(result.startswith(unicode('<div></div>', 'iso-8859-15')), True)
 
 class ZopePageTemplateFileTests(ZopeTestCase):
 

lib/python/Products/PageTemplates/unicodeconflictresolver.py

@@ -84,7 +84,7 @@ class PreferredCharsetResolver:
 
             try:
                 return unicode(text, enc)
-            except UnicodeDecodeError:
+            except (LookupError, UnicodeDecodeError):
                 pass
 
         return text