Translation:I have plans tonight.
I think this sentence is so smart! "I have a thing/things tonight" = "I have plans tonight" (^_^)
This is one of those that should be limited to the word bank as there are too many correct ways to translate. A few examples, I am occupied tonight, i am busy tonight, i have things to do tonight, i have plans tonight, I will be predisposed tonight etc.
I agree. "I have plans for tonight," seems more like natural English to me.