Student or Learner
someone says to me "have a good weekend!" and i want to wish the same to him/her.
the only thing i know to say is "you too!".
i would like to answer in a informal way, but differently.
what could i say?
"you too" is the best response, and the only one that sounds natural to me.
"same to you" is possible, but that phrase is often used in responding to an insult.
I don't think you need to worry about this.
This kind of expression is called, technically, "Phatic communion," just used as social lubricant, being friendly. It's like "Hi, how are you?" (You're not really asking about his health.) or "Nice day, isn't it?" You're not really asking his opinion of the weather."
So your friend isn't really telling you what kind of weekend to have.
"you too" works just fine. If you want variety, try saying "you too" in different tones of voice.