DS is almost 20 months and has a recognizable amount of words in two languages (I've lost count, but it's more than 50 each), He learns new words almost daily. And uses them in practice. His receptive language has always been great.

He refuses to say Hi. He says bye-bye. He knows what Hi means, but prefers to wave and when we suggest he say HI with his words, he shakes his head and says no.

There are other words that he refuses to verbally say too... normal? Do they outgrow it? What can we do to encourage?