They say that usually only a mother understands her child's baby language. I guess thats true too for any child minder who is with the child a lot, dads, grandparents, babysitters, maids, siblings.
My boy has just started to talk a lot recently and being closest to him throughout the day, most days, usually I know what he wants when others don't. In fact, his sister knows even better than me most of the time. Sometimes I have to ask her "What does baby want?" when he mumbles something and she usually knows exactly what he wants. Lol!
For example, one of the things he says which only me and my girl understand is this.