Anyone can speak Troll. All you have to do is point and grunt.Troll language is supposedly nothing more than simple grunts that only Trolls seem to be able to interpret, though skilled magical multi-linguists such as Barty Crouch could understand them. Trolls understand only a limited number of Human words, and some smarter ones can be skilfully trained as security trolls. Professor Quirrell had a gift for communicating with trolls, and then used it to set one loose in Hogwarts School of Witchcraft and Wizardry in 1991 in an effort to steal the Philosopher's Stone.
Mountain trolls have been known to tame and ride Graphorns, or at least try to ride them. Graphorns don’t seem to be very keen on the idea.