Bilingual children sometimes take longer to speak depending on how both languages are being used in your household. However, most children will pick one language for their main one in the beginning. That is usually the language the child has the most exposure to hearing. Language development for bilingual children usually is not that far behind language development of a child in a monoligual home, even though they are processing two languages. Speaking fluency in both languages will occur sometime between the ages of 5 and 7. At two, I think your son should have more than 12 words in at least one language. I would recommend having him evaluated.
We are a bilingual family as well. Before my son was born, my husband and I decided the ground rules we would use in the house concerning language. My husband is Japanese, and I am American. My husband can speak English fluently, although his grammar sometimes reveals that he is not a native speaker. I can speak Japanese fluently enough to get myself in and out of trouble most of the time. We speak English together mainly. (We are currently living in Japan, and we have lived here for my son's entire life. So, English is technically the second language for us. )
We decided to only use our native language when speaking with our son. (I only speak to my son in English, and my husband only uses Japanese.) This is the best way to insure that your child will pick up native pronunciation and grammar in both languages. We read books to our son from a very young age. I was reading 15+ books a day to him when he was 6 months old. I read to him before every naptime and at bedtime. My husband read 1 or 2 books to him at bedtime only. Our son completely dropped his naps when he was 3. To keep the reading in place, we have a 30 minute story time daily, plus 1 or 2 books from me at night and a bedtime story from his dad. Reading to your child will build up his vocabulary, set the early stages for him to learn to read, increase his ability to focus on something...
How much did you expose him to language? I talked about everything to my son. I narrated what I was doing when he was younger. When he started speaking, I would often repeat what he said, and then replaced it with the word he was wanting to say. He would hold something up or point to something, and I would tell him. I tried to get him to repeat it back. I would ask him what things were all the time. For example: "Do you know what that is?" "That's a cat." He loved pointing to our cat. Does your son seem interested in communicating with you? If he doesn't seem to want to talk, that would be a clear indication that you need to get him some help.
Since my son spends the majority of his time with me, English is the language which he uses most of the time. Now that he is 5 years old, and in a Japanese only Sunday school class, he is starting to speak more Japanese with his dad. I am guessing that once he begins school, the Japanese is really going to take off. Bilingual children instantly know which language other people around them can and can't speak and adjust accordingly.
I don't know what route you took in exposing your son to both languages, but I would highly recommend only speaking your native language with him. Can he respond correctly when spoken to in each language? It's not too late to go back and only speak to him in your native langauge, especially since he isn't speaking much on his own yet. I would also start reading to him often. If you haven't read to him much, I would probably start out with 1 book at a time, and gradually increase the number of books. I also would try to get him talking about what is in the book. Ask questions for things he finds interesting in the story. Talk about the story and role play it too. All those things will help increase his vocabulary.
Hope that helps a little. The bilingual, bicultural family has double the troubles, but double the fun too!