You searched for: “xenoglossia
xenoglossia (s) (noun) (no pl)
The alleged power of a person to communicate with others in a language which he/she has never learned; xenoglossy: Linda wished she possessed the ability of xenoglossia so that she wouldn't have to take classes to learn that language.

Xenoglossia can also be the knowledge of a language which supposedly has never been studied by certain people.