Here's my non-medical opinion:
Kids talk slower than others for a variety of reasons, hundreds of them. But it really boils down to these:
1) Does he have to talk?
-Do you make him show you what he wants, say 'Please' and 'Thank You' when he wants something and gets it? Or do you just give him anything he wants when he starts whining or gets frustrated?
If he really wants those Oreos, he'll learn how to say please very quickly when he figured out that's the quickest way to get it.
Part of the problem that comes up with this is that parents know their kids so well, they can predict what their kid wants. If your child doesn't need to tell you what he wants, ask for it (Please) and Thank You when he gets it... then he won't.
Make him show/tell you what he wants, and try to correlate the words he needs to use consistently while you do it.
2) The Pacifier
Get rid of it, if you haven't already. How can a child learn how to talk if he's too busy sucking on a pacifier all day? Even worse, if he's trying to talk while it's in his mouth, then you may run into lisp issues or speech irregularities.
The basic purpose of the Pacifier, let's be honest, is that so we the adults don't have to listen to our kids cry. Put it in, and bam.. no crying. We're really doing ourselves a disservice by using them after 4-6 months old.
3) I'm not a strict parent by any means. I let him get away with a lot at 19 months because I wanted to him to find out first hand what would happen if he did stupid things. Want to stand on the tennis ball? Well, be prepared to a big headache! Want to kick the dog? Well, how did it feel when he but you in the nose?
Since I'm not too strict about a lot of things, he knows I mean business when I am serious about something. He won't get his hands on any piece of food without asking for it, saying please, and saying thank you when he gets it. After a while he figured out what each piece of food was called, and we added that. "Cracker Please!!!" "Basketball PLEASE!!!
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The way I generally feel is after about 6 months of age, the honeymoon is over. You have a kid now, not a novelty (Come on, we all felt that way). Your friends have already seem him/her, now it's time to teach them about life. If they're 12 months, act like they should know things a 15 month old kid knows. Ever notice the 3rd kid always learns the quickest? You want to him to learn, so he does.
If he understands what you're saying, then he can say it. You just have to find your own mother/son way of forcing him to do it, in order to get what he wants.