YOU SAID:
you must buy the taco tonight
INTO JAPANESE
あなたは今夜タコスを買わなければなりません
BACK INTO ENGLISH
You have to buy tacos tonight
INTO JAPANESE
今夜はタコスを買わなければなりません
BACK INTO ENGLISH
I have to buy tacos tonight
INTO JAPANESE
私は今夜タコスを買わなければならない
BACK INTO ENGLISH
I have to buy tacos tonight
That didn't even make that much sense in English.