Actually I see this as an interesting question.. I've had parrots all my life. Currently I have two cockatiels, two budgies and a red rump parrot. They all talk. Some more than others.
Some words they say are just repeating, but without a doubt they do know what they are saying much of the time.
My oldest cockatiel says bye-bye mama when I leave. He also says Hello when he sees someone enter. My kids are grown and he knows them all by their names and when he sees one of them,even after along time, he will call them by their proper name. He definitely knows who is who. There are many other instances I can tell you about if you want to.
Others will say they don't really know what they are saying, but I live with these intelligent, feeling creatures and I KNOW that they truly understand much of what they are saying.