I can think of at least one or two instances in my own life where, as I was praying, I was wanting to fully express my strong emotions to God about a particular troubling issue I was dealing with at the time. And, when words failed me, I resorted to unintelligible sounds. And, I believe God heard that, and of course knew what was being expressed from my heart. He knew it before I opened my mouth.
But as I reflect on those times, I know that I was not speaking in some angelic or heavenly language. Also, I think that if I would have opened up the bible to the book of Psalms, and began praying scripture, I would have been able to more fully express myself, and would have walked away from that being more satisfied knowing that God had heard my prayer and understood what was in my heart.
Scripture is always better.