If your child is in a home with two languages, it will take more time for him to talk, but when he finally does talk, he will be vey fluent in both languages. Also, boys take longer than girls which is normal. I don't know if this is your situation, though.
My son had the same problem that you are writting about and we are in a single language home. At 15 months of age he had two or three words which concerned his pediatrician. Then at 18 months he had a few more words. Finally at his 2 year check up, the doctor gave me the number for the county regional center for evaluation. (This is a free service.) I followed through with his advice and am glad I did. My son was tested at 25 months. He was having articulation problems (speaking) which made it hard to understand what he was saying. However, his language skills (what he understood) were that of a 36 month old. We only did therapy for 3 months, but that was enough for him to get over the hurdle. Now he is 32 months old and talks like you can't beleive. The therapist gave us crazy mouth exercises and silly word games to do at home, which apparently did the trick.
He is still in a learning stage of speech and we help correct him all the time but the pressure is off because he has so many words to communicate with. I do think he would've have learned eventually to speak, but he was getting so frustrated that he could't and we didn't want to create a bigger problem. Having the tools to help him really helped us.
Good luck to you!