The thing about "unknown tongues" is (conveniently) there's no way to prove or disprove it. When tongues first became a big thing in the early 20th century, the belief was that tongues were human languages that had not been previously learned, but were supernaturally imparted. However, when missionaries set out to demonstrate it by traveling to foreign lands to preach the gospel in the native tongues of the people, they fell flat; no one understood a word they said. It wasn't long after this they retooled and tongues became an unknown or angelic tongue. No one could say otherwise because how could they?
To me this is the most clear and convincing evidence that ecstatic utterances are not the real thing.
To me this is the most clear and convincing evidence that ecstatic utterances are not the real thing.