I think he did understand what he was saying. Since Fun with Dick and Jane, he started to learn spanish. And his speech was in a perfect spanish. And it was made in Carrey, it was funny as hell, and with his trade mark... I was surprised by it. But he definitely knew what he was saying!! ;D
"ME HACE GRITAR DE PLAACEEER!!!" (Watch this sentence on the video and then you will be sure. )