My gut says you would need vocal cords or something to be able to make slight differences in pitch and tone to your voice, that is something that's built into the architecture of your body. Other animals have it but not to a degree that they can make hundreds of different sounds to make thousands of different words. So in terms of mental capacity we only know the size of their brain not really how it was wired but in terms of the architecture of their throat and mouth I think fossils would show that.
My gut says you would need vocal cords or something to be able to make slight differences in pitch and tone to your voice, that is something that's built into the architecture of your body. Other animals have it but not to a degree that they can make hundreds of different sounds to make thousands of different words. So in terms of mental capacity we only know the size of their brain not really how it was wired but in terms of the architecture of their throat and mouth I think fossils would show that.
What do you mean with complex language? Do gorillas have it then probably yes. If more human level then probably no