First of all, we Bible believers believe in a word for word meaning, not necessarily a strictly literal word for word translation. Sometimes the literal translation would not make sense to us.
ALL translations into another language require the "addition" of certain words for a passage to make proper sense. Why? Because the Hebrew and Greek languages are often elliptical languages. That is, they sometimes omit the Subject or the Verb, or the Direct Object, the Indirect Object or even the word "not" when the text requires it when placed into another language.
The King James Bible translators were honest enough to put most of these "added" words in italics so you could see where they did this. Versions like the NASB, NKJV, ESV, NIV, NET, Holman Standard ALL still "add" those words but they do not always put them in italics so a person reading them is not aware of this.
The immediate context of 1 Corinthians 14 necessitates the "adding" of the word "unknown", because what was being spoken was not a known language to those who heard it. The example of tongues being spoken in Acts chapter Two is quite different. There the people understood what was being said in their own languages, without the need of an interpreter. Here, in 1 Corinthians chapter Fourteen, the type of tongue being spoken was not understood by anyone present in the church meetings. A simple reading of the whole chapter will make this abundantly clear.
Notice: "he that speaketh in an UNKNOWN tongue speaketh not unto men, but unto God, for no man understandeth him...he speaketh mysteries"; "except ye utter by the tongue words easy to be understood, how shall it be known what is spoken?"; "if I know not the meaning of the voice...he that speaketh shall be a barbarian unto me"; "if I pray in an unknown tongue...my understanding is unfruitful"; "he understandeth not what thou sayest"; "if any man speak in an unknown tongue...let one interpret, but if there be no interpreter, let him keep silence in the church."
What was being spoken was obviously an "unknown tongue" and unless one was present who had the spiritual gift of interpretation, then what was being said could not be understood or known by anyone there.
Once again, the KJV is superior.
i don't have to know anything about tongues at all -- i don't even need to be able to speak English or Greek -- to see clearly that the KJV has inserted the word "unknown" into the translation here, but "unknown" is not in the Greek text that was being translated.
to its credit however, the KJV does put "unknown" in italics -- indicating that it's an insertion not found in the originals.
