All of the Seven (Nico included) have their own language.
Leo rants in Spanish and creaks and squeaks with Festus
Piper rants in French
Annabeth rants in Ancient Greek
Jason rants in Latin
Hazel rants in Old fashioned Louisiana French
Frank rants in Chinese
Nico rants in Italian
And, as always, we've got Percy . . .
Who rants horse and sea creature