I always thought that also but I dont think thats the case. Look here.
1 Corinthians 13:1 Though I speak with the tongues of men and of angels, and have not charity, I am become as sounding brass, or a tinkling cymbal.
That indicates to me that it is not just the tongues of men.
Everyone that I hear speak in tongues speaks something that does not sound like what others speak. And they claim it’s their own private prayer tongue, for themselves only.
How many tongues of angels are there anyway?