Thanks for your reply, but I'm don't think the page solved my problem. For one thing, I NEED the "Automatically switch to a document's input method" box to be checked.
Let me further describe the way I use Alfred:
I have three windows with different language settings, 1) TextEdit, always in Chinese; 2)Alfred, always in English; 3) Dictionary.app, always in English. (I must reiterate that, this is the way it used to be, and I started to have this problem only with the recent few versions of Alfred.)
While typing Chinese in TextEdit, I might want to Google something, so I use opt+space to activated Alfred, type in English keyword, then ctrl+enter to let Alfred send me to Chrome.
Now, I understand that if I've let the "Automatically switch to a document's input method" box unchecked, whenever I switch back to TextEdit, the language will still be Chinese. But the problem is, I also want to keep the search box of Dictionary.app in English. Uncheck "Automatically switch to a document's input method" means, I will have to manually switch to English every time I use Dictionary.app. And that's really inconvenient.