It has often been said that people can speak in languages that were not formerly known to them. Arguably the most often recited example of this is in the context of demonic possession. For example, those supposedly possessed by malevolent spirits apparently can and regularly do speak in languages they do not know — so often has this happened that it is evidently one of the four criteria typical for "demonic possession":
True demonic or satanic possession has been characterized since the Middle Ages, in the Rituale Romanum, by the following four typical characteristics:
- Manifestation of superhuman strength.
- Speaking in tongues or languages that the victim cannot know.
- Revelation of knowledge, distant or hidden, that the victim cannot know.
- Blasphemous rage and an aversion to holy symbols or relics.
For whatever reason, it is usually Latin. In any case, the key feature is that it is a language unknown to the supposedly possessed speaker, and the phenomenon is called xenoglossia (not to be mistaken for glossolalia, or speaking in tongues, or bilingual aphasia being the transposition of linguistic competence).
The ability to speak in languages previously unknown to a speaker seems to be a testable hypothesis, particularly with modern day recording technology.
Just for clarity, here is a citations defining the claim:
Xenoglossia: Xenoglossia is the sudden and abrupt ability to speak in multiple languages (2). It is imperative that the demonologist look for signs that back up the fact that the suspected victim of demonic possession did not have prior knowledge of such languages or any kind of fluency in the languages exhibited before denoting the appearance of multiple language usage as an indication of possession. It should be noted that in some reported cases of mental illness, an individual can present the ability to suddenly speak in previously unlearned languages. Instances of savantism and genius should also be ruled out before xenoglossia is deemed a sign or symptom of demonic possession.
Is there any evidence regarding the existence of this phenomenon?