I've been under the impression that Zechariah Sitchin did the translation and research himself. Here is a link to a site that claims he does have the ability to translate Sumerian tablets.
http://www.zechariasitchin.com/
There are many scholars and educators who have done research as to the authenticity of Mr. Sitchin's work. Lloyd Pye is most convincing IMO. Also, it should be noted that Robert Harrington, who had worked at NASA for quite a long time, verified the existence of Nibiru/Planet X in an interview with Sitchin. Shortly thereafter, Harrington allegedly committed "suicide".
I have to admit that I am most definitely a believer in the Sitchin material, as it rings much truer to me than the religious teachings I've had my entire life, and it has given me the opportunity to become more spiritual than I ever would have had I not read his books.