As in anything, may God cause the increase, but at this site, one can see why "unknown" was inserted in reference to tongues in the KJV to testify of the new tongue but unknown to the speaker. It addresses most common errors and misreading of scripture in 1 Corinthians 14th chapter by those who believe tongues are for private use, but again, only the Lord Jesus Christ can help them see the truth in His words to know Paul's actual message.
Speaking In Tongues - Unknown Tongue Speaking by Commentary
Speaking In Tongues - Unknown Tongue Speaking by Commentary