Index: lib/redmine/unified_diff.rb
===================================================================
--- lib/redmine/unified_diff.rb	(revision 11169)
+++ lib/redmine/unified_diff.rb	(working copy)
@@ -207,10 +207,16 @@
         while starting < max && line_left[starting] == line_right[starting]
           starting += 1
         end
+        while line_left[starting].ord.between?(128, 191) && starting > 0
+          starting -= 1
+        end
         ending = -1
         while ending >= -(max - starting) && line_left[ending] == line_right[ending]
           ending -= 1
         end
+        while line_left[ending].ord.between?(128, 191) && ending > -1
+          ending -= 1
+        end
         unless starting == 0 && ending == -1
           [starting, ending]
         end