You asked

Can the pure language be made up exclusively of the pure words of the LORD ?

The first thing that came to my mind after reading your question was "unknown tongue"

"Unknown tongue"  is mentioned 6/6 times in the King James Bible.
6= mans #

1 Corinthians 14:2 KJV
For he that speaketh [in] an unknown tongue speaketh [not] unto men, but unto God:
for no man understandeth him;
howbeit in the spirit he speaketh (mysteries.)

1 Corinthians 4:4 KJV
He that speaketh in an unknown tongue [edifieth himself;] but he that prophesieth edifieth  the church.

14:13 KJV
Wherefore let him that speaketh in an unknown tongue [pray] that he may (interpret.)
14:14 KJV
For if I pray in an unknown tongue, my spirit prayeth, [but my understanding is unfruitful.]
14:19 KJV
Yet [in the church I had [rather] speak five words [with my understanding,] that by my voice I might teach others also, [ than ten thousand (words) in an unknown tongue.]
14:27 KJV
[IF ANY MAN] speak in an unknown tongue, [let it be by (two,) or at the most (three,) and [that] by course; and let ( one interpret.) ]

To speak in an unknown tongue (to my understanding) of the above verses is a mystery language. Such can be abused and mis-used as is being done in [many] of our churches today.
It seems to be a "spirit language" when one is in the spirit, one will speak this language, but is not understandable to men. Thus the need for [two or three to interpret, in order that [all] in the church might understand and be edified.

This so called "speaking in tongues" practiced by many churches is not biblical and is being abused and misused.
It is guile !
There is [A] spirit there, but it is NOT the Holy Spirit.

How can we know this?
Because our God is NOT a God of confusion.
Continuous babbling by a whole congregation is CONFUSION.
It is a [spirit of confusion !] One in which the complete disruption of a Pastors message can and does occur.
I personally have witnessed this happen.

Is this unknown tongue the pure language?
I cannot say, I have no scripture that would prove that it is.
Personally I think it [will] be a SPIRITUAL language, because God is Spirit, and yet he [is] also man.
 
I believe it was Jesus Christ known as "The Word " whom John saw in Rev 4:1, I believe it was Jesus Christ/ The Word whom Jacob wrestled with, and also whom Daniel saw stand in the midst of the water, and I believe that it was The Word who walked with Adam and Eve in the Garden, and who spoke with Abraham concerning Sodom and Gomorrah, even as the garden of the Lord, also like the land of Egypt, and He is The Holy One who shines forth from Paran.

" The Word "
to us a word is [one] of many that make up a sentence, which is language.
Perhaps the language will NOT be spoken, but through the mind and heart.

We will simply think and we will be where ever we seek to go,
and think and we will communicate one with the other.
In that God knows the hearts and minds of men.
We know that we shall be like him. 1 John 3:2 KJV

Job 40:9 KJV
Hast thou an arm like God? or canst thou [thunder] with a [voice] like him.

John was asked to NOT write what the 7 thunders of God said. Rev 10:4 KJV

1 John 3:2 KJV
Beloved, NOW are we the sons of God, and it doth not yet appear what we shall be: but we know that, when he shall appear, we shall be like him; for we shall see him as he is.

Oh what a day of rejoicing that will be ! When we all see Jesus, we will sing and shout the victory.

God Bless you
KML