YOU SAID:
there will be cake tonight
INTO JAPANESE
今夜はケーキがあります
BACK INTO ENGLISH
I have cake tonight
INTO JAPANESE
今夜はケーキを食べます
BACK INTO ENGLISH
I'm eating cake tonight
INTO JAPANESE
今夜はケーキを食べます
BACK INTO ENGLISH
I'm eating cake tonight
That didn't even make that much sense in English.