my 19 month old can maybe say 15 words, and generally i have to prompt him.
he still has his own little language for things, the tirck i found is not to talk for them. Keep prompting them to tell you what they want, what things are etc. Its amazing to see exactly how much we talk FOR our kids.

I wouldnt worry, i used to worry about his development but i realised its my expectations i am placing on him - and sometimes that is a really bad thing.