I found this post on StompTokoyo's Movie Search forum:
I kind of remember this film I saw when I was a kid it envoled a dark blue/black dragon that learnt to talk by listening to people in the underground, a scientist comes looking for him with some army guys. But he joins a street smart kid (I think called zack)
We might be able to help as well. I've already looked through IMDb's list of dragon films from 1900-1990 with no luck. Any ideas?
I must admit the plot sounds interesting...