Tongues as an Unknown Language: Where in scripture can you make a case for speaking in tongues being an unknown language, pehaps that of angels? [I Corinthians 14:2 & 13]. Tongues as a Known Language: Is tongues in the book of Acts at Pentecost a known language? [Acts 2, Acts 10, Acts 19, I Corinthians 14, Jude 1:20].