Animals cant speak normally (i.e a animal companion cannot speak a language even with high intelligence), it has to be awakened for this to happen. However, since the creature was a human, it should technically count as awakened as so should be able to speak no matter what form it is in.
Also, dispel magic does not work on Baleful Polymorph, it has a permantant duration but is an instaneous effect. You litterally need break enchantment. Whats worse is Baleful Polymorph specifically prevents any other polymorph effects from working on the creature so you can't even polymorph it into another form.
