[kombookcha]

This is already sort of in Jurassic Park 3, which features a 3D-printed velociraptor larynx that can be blown into to reproduce vocalizations remniscent of the velociraptors in the movie. At the end of the movie Alan Grant blows in it, confusing a pack of velociraptors.

There's a specific call that the movie has established as velociraptors in distress calling for help/backup from the pack, and Alan attempted to reproduce it when cornered at the beach to basically bluff/intimidate the pack into avoiding a fight. It coincided with the arrival of a helicopter, and the combined effect made the raptors run away.

Not explicitly a language as such, but specific calls with understandable, relatively complex meaning to the dinosaurs, that can be (sorta) understood and leveraged by humans.