Question

Could someone please help me decode this Shakespeare quote? "If music be the food of love, play on,
Give me excess of it; that surfeiting,
The appetite may sicken, and so die."

English is my fourth language, thus Old English is even more difficult to me.

Answer 1

This is Early Modern English, not Old English which was the language of the Anglo-Saxons.
Have a look at:
http://en.wikipedia.org/wiki/Old_English

Answer 2

Oh, right! My apologies, I mix them up often.

Answer 3

This is spoken by Orsino in Shakespeare's Twelfth Night. Here is the best that I can translate it.
"If music be the food of love, play on"
This is a metaphor. It is comparing the way that food feeds your hunger to the way that music feeds feelings of love.

"Give me excess of it; that surfeiting,
The appetite may sicken, and so die"
Is continuing the metaphor, basically saying: If music is what feeds love, let me overeat so that I will never want to feel the pain of love again.

Orsino is referring to his love for Lady Olivia who always sends away his messages of love and rejects him.
Have you ever sat down in a bad mood and listened to sad music just so you can feel your own emotions a little more? That's what Orsino is doing. He wants to be overwhelmed with his sadness because he thinks that if he feels it all now, he will never have to feel it again.

I hope that helped. Awesome that you know so many languages. Good luck.