The answer is "if (verb suffix)" is it supposed to be because "if" itself doesn't work?
In English, "if" is a separate word. In Klingon -chugh is a suffix and must be attached to a verb. The "(verb suffix)" tag was added to help clarify that. If you just type "if" as the translation it should accept that.
I've added "if" on its own as an answer now.
(The previous alternatives tried to include that but there was an error in the "code".)