Sayyed Muhammad Husaini Ragheb, Sayyed Muhammad Husaini Ragheb has a BA in Law from Guilan University, Iran and has also undertaken Hawzah studies in Qom. He is a Cultural Affairs director of Ethics Group of Al-Mustafa Open... Answered 2 years ago

Simply reply by Alaikum Assalaam wa Rahmatullaahi wa Barakaatuh
in fact this is a dua
you are saying "May God's peace and blessings be upon you" in Arabic
So if this friend of yours is acting that much friendly and wants to greet you with your Islamic culture do treat him/her in the same way and DO translate it for him/her.