This is the oldest race that ever roamed middle earth in the third age, and they were called enyd or Onodrim in the ancient tongues. They took their wish to speak when they met the Eldar (the first elves), but their tongue was slow, repetitive, cumulative and required a lot of time to say anything, and not even the wisest elves dared to try and understand it let alone speak it.
But Ents were wise and intelligent and despite nobody being able to learn their tongue, they easily learned other tongues and never forget them.
