Hi L.,
I understand you completely!!! My son will be 2 in Dec 15th. And he understands wonderfully, he knows believe me!!! He babbles a lot (u know their own language) and u can see him expressing himself thru his face movement. He has said in the past, mama, papa, dada, mas (more in spanish), no, oh no, oh wow, yeah, yeahie. Simple stuff like that, but he gets to his time that he will say mama only and babble for the longest, and now all he wants to say is "oh, no" or "mama" but a lot of babbles....I'm really not worried, because my mom and other people have told me that all kids are different, if you feel he understands you and tries to communicate w/you somehow or says little things, then he should be fine. Also, I have heard that when he is the only child is harder for them to talk, especially when like mine he doesn't have any other children interaction, just us adults and tv. Just give it time and if I would say by Feb or March he just stays using one or two words then really take it to do some tests..just to make sure...
But I would suggest to listen to your heart if you really feel that is not right, then go demmand to his/her doctor to do some tests, that's your child and you are the only one that knows what's right for him/her!!! Good luck!!