Wa iyyakum (And to you)
Assalaamu alaikum click on the link given below you'll find lyrics just below the video Jazaakallah http://www.youtube.com/watch?v=y6Z7WjqkV_0
Islam (Muslims) is a religion, not a language. but if you mean Arabic it is "Shukaran" The answer, above, is correct. Now, the real way you should thank any Muslim, is not to say "thank you", but you're supposed to say "May God reward you with good" In Arabic: Jazaak Allahu Khairan.