all requests are utf-8. Don't use the external encoding.

actionpack/lib/action_dispatch/http/upload.rb

@@ -33,10 +33,9 @@ def size
       
       private
       def encode_filename(filename)
-        # Encode the filename in the default_external encoding, unless it is nil or we're in 1.8
+        # Encode the filename in the utf8 encoding, unless it is nil or we're in 1.8
         if "ruby".encoding_aware? && filename
-          encoding = Encoding.default_external
-          filename.force_encoding(encoding)
+          filename.force_encoding("UTF-8").encode!
         else
           filename
         end

actionpack/test/dispatch/uploaded_file_test.rb

@@ -14,12 +14,7 @@ def test_original_filename
     end
     
     if "ruby".encoding_aware?
-      def test_filename_should_be_in_default_encoding
-        Encoding.default_external = "UTF-16LE"
-        uf = Http::UploadedFile.new(:filename => 'foo', :tempfile => Object.new)
-        assert "UTF-16LE", uf.original_filename.encoding.to_s
-        
-        Encoding.default_external = "UTF-8"
+      def test_filename_should_be_in_utf_8
         uf = Http::UploadedFile.new(:filename => 'foo', :tempfile => Object.new)
         assert "UTF-8", uf.original_filename.encoding.to_s
       end