YOU SAID:
I am going to do a great thing for you
INTO JAPANESE
私はあなたのために偉大なことを行うつもり
BACK INTO ENGLISH
I am going to do great things for you
INTO JAPANESE
私はあなたのためにすばらしいことをするつもりです
BACK INTO ENGLISH
I am going to do wonderful things for you
INTO JAPANESE
私はあなたのために素晴らしいことをするつもりです
BACK INTO ENGLISH
I am going to do wonderful things for you
That didn't even make that much sense in English.