I don't know if it's what you looking for but I found this at "Ask about Middle Earth" on tumblr:
first insult (which he says directly to Thranduil) translates into “Die a death of flames." The second insult (which he shouts from the cells) translates into "I pour excrement on your head.”
You can read all of the rest here: link

Hey basically said i'll shit on you and legolas's heads