Mermish is a curious language that is specifically adapted for use underwater. When underwater it sounds much like English, or perhaps even like any other language (Harry Potter is the only one who is personally shown in the books to hear the merpeople); however, out of water the language changes to a screeching, harsh and raspy sound.
It is unknown whether non-merpeople who can speak mermish sound the same as merpeople underwater i.e. whether or not they retain an accent (though they probably do) though it is known that non-merpeople can speak it. Dylan Marwood and Albus Dumbledore were known non-Merperson speakers, and Percy Weasley claimed that Barty Crouch Snr could also speak it.
- Harry Potter and the Goblet of Fire
- Harry Potter and the Goblet of Fire (film) (Only heard from golden egg)
- Harry Potter and the Goblet of Fire (video game) (Only heard from golden egg)
- Harry Potter and the Order of the Phoenix (video game) (Only heard from golden egg)
- Harry Potter and the Half-Blood Prince
- Harry Potter and the Deathly Hallows
- Fantastic Beasts and Where to Find Them
- Wonderbook: Book of Spells (Mentioned only)
- Harry Potter: The Creature Vault (mentioned only)