Dear [name of addressee here],
I have received the invitation you sent me a couple of weeks ago. My apologies for responding late as I have been very busy at the office for the past few weeks. I am very honored to have been included in your wedding guest list. It would be a great loss on my part if I would not be able to come in a special event of your life.
This is to manifest my acceptance of your invitation. I will be coming together with my wife who is equally excited about your wedding. I hope it would not be a big hassle on your part to accommodate the both of us in your wedding.
I already know the details of your wedding, and you can expect us to behave as our sign of respect to you and your would-be wife. See you next week and best wishes!
[name of sender]