I think it is hard for the developer of Alfred to reproduce such problem.
I found this problem may come from the different UTF-8 sets in my system.
After remove all other languages in the system preference of Mac and restart the system.
(i.e. change the locale to zh_tw.UTF-8)
the search result for Alfred and spotlight is the same if I use some traditional Chinese Characters to find file.
However, if I use characters of simplified Chinese to find a specific file , Spotlight is able to find the file I need, and Alfred finds nothing.
I have no idea how to fix this problem by setting.
