A Polyglot can speak languages instinctively just from hearing them and can mimic other peoples' voices, though elves with other abilities can learn to mimic as well. Polyglots often have another special ability.
Lady Gisela - Keefe's mother and Lord Cassius's wife. She was the leader of the Neverseen until Fintan Pyren takes over. She used her ability as a Polyglot to imitate Lord Cassius to make people think he was one of the leaders of the Neverseen. This works until Keefe knocks her hood off, revealing that it was her, not Lord Cassius who was a leader of the Neverseen.
Councillor Clarette - She can control animals with her voice. She is arguably the most powerful Polyglot the elvin world has ever known and has had hundreds of years of practice. She controls the arthropleura on the attempted rescue of Prentice from Exile in Neverseen.