There is a video on the Internet now showing twin boys about 14 months old talking to each other. They hold an entire conversation of babbling. Each takes his turn and then waits for the other to respond. This conversation is complete with hand gestures and laughter. It is a delightful video to watch.
This type of conversation between twins is not unusual. It is called Twin Talk. Many twins enter school carry on an entire conversation, but they are the only ones who can understand the speech. They must be taught the English language so they can communicate with others. Some drop the Twin Talk when they learn language. Some however, continue the Twin Talk when speaking to each other. It is like a secret code that binds them for life.
If you have the opportunity check out the video.http://www.wimp.com/babyboys/