YOU SAID:
Thou mustn’t eat cake
INTO JAPANESE
ケーキを食べてはいけません
BACK INTO ENGLISH
Don't eat cake
INTO JAPANESE
ケーキを食べないで
BACK INTO ENGLISH
Don't eat the cake
INTO JAPANESE
ケーキを食べないで
BACK INTO ENGLISH
Don't eat the cake
That didn't even make that much sense in English.