我请客:
I'll treat you.
I am treating you. (比较礼貌)
I am paying.
It's my treat.
Let me treat you.
It's on me. (一般与被请客的人不熟,或者是吃完以后说)
Let me get this. (吃完后)
Let me take care of the bill. (吃完后)
其他人请客:
He will pay for it.
She is paying the bill.