In British English dinner is not necessarily an evening meal. It's the largest warm meal of the day. So if you're only having tea in the evening lunch could turn into dinner. So it depends. If "cena" is an exact translation of that it wouldn't necessarily be "tonight".
as far as i am concerned i translated literally and was marked correct - but to me it sounds like not that good English when the word 'today' finishes the sentence (this English sentence of mine probably doesn't sound that good as well^^)
"Dinner" is a trickier word than most people realize. In some places it means "lunch" and in others it means "supper." So I translated it as fish for dinner tonight, since in Italian it refers to the evening meal.