YOU SAID:
My friends are going to come to my birthday
INTO JAPANESE
私の友達は私の誕生日に来るつもりです
BACK INTO ENGLISH
My friend is going to come on my birthday
INTO JAPANESE
私の友人は、私の誕生日に来るつもりです。
BACK INTO ENGLISH
A friend of mine is going to come to my birthday.
INTO JAPANESE
私の友人は、私の誕生日に来るつもりです。
BACK INTO ENGLISH
A friend of mine is going to come to my birthday.
You've done this before, haven't you.