My daughter is a bit over 15 months and doesn't say ANY words at all yet. Her pediatrician says that yes, her speech is a bit delayed, but that it's nothing to be worried about.
Sounds like she has the same skills as far as understanding language as your son. She just doesn't use her own language. We did have her hearing checked just to rule out that cause and it's fine. I also had an interview with First Steps for possible speech therapy. The woman I spoke with (who was VERY nice and really seemed to know her stuff) said that they very rarely will begin speech therapy before 18 months unless the child has other developmental delays as well.
The only advice my pediatrician and the woman from First Steps gave us was to make sure to label everything (not like put signs up, but say the words for every item and action we use) as well as read books and sing songs often. I feel like we've been doing all of these things all along but we're definitely making a concerted effort to do it.
Another possibility that my pediatrican gave for why she is slow to talk is that she is pretty advance physically. Her motor skills are excellent, climbing, running, spinning, walking backwards, using a spoon and fork, etc. He says that often a child that excels in one area lags in another but will eventually catch up.
It's frustrating right now, I know my daughter is throwing more fits and tantrums because she is getting frustrated by not being able to communicate with us than she would if she had more developed language skills.
I'm just going to hang in there. Do what we can, and if she hasn't progressed at 18 months we will have her evaluated by First Steps for speech therapy.
R.