The plea and command is to follow after charity, otherwise spiritual gifts including speaking in “tongues” would be exercised in vain.
1 Corinthians 14:1 KJV Follow after charity, and desire spiritual gifts, but rather that ye may prophesy.
The “unknown tongue” is recorded in the King James Bible, so I am not going to go with the whole “the word unknown was not in the originals” argument. If it is in the KJB, it’s the Word of God, period. So we need to look further into this word “unknown.”