While reading Psalm 68 this morning, I came across this verse which uses the name "JAH":
Sing unto God, sing praises to his name: extol him that rideth upon the heavens by his name JAH, and rejoice before him. (KJV Psalm 68:4)
Elsewhere in the KJV the Psalms use the title 'God' but in chapter 68 verse 4 it uses the name 'JAH'.
The NIV, ESV, and NLT all say "His name is the LORD".
I am familiar with the explanations that YHWH, the name of God, is unpronouncable and that the Divine Name was not to be spoken aloud. I also understand why the Divine Name has been substituted with 'God' or 'the Lord' in most English translation.
I found a related question in Biblical Hermeneutics but I was unable to understand the answers given, mainly because I know nothing about Hebrew in particular and grammar in general. In Psalm 68:4 and Psalm 135:1 how are contractions formed in Hebrew and how does YHWH become Yah?
I would like to avoid convoluted explanations and keep this question simple if possible - what is the reasoning or explanation behind the KJV translating the name of God as Jah in Psalm 68:4? Is the manuscript being used here in the KJV different to the manuscripts being used in other translations? And why only in this one verse?
Edit: I went back to the question I referred to and found this:
Psalm 68:4 expresses the name of God as Yah. This seems obvious related to the name of God as he expounded it to Moses in Exodus 3:14. We also see the two directly connected in passages such as Psalm 135:1:
Praise the name of YHWH!
Praise him, you servants of YHWH,
Brown-Driver-Briggs says Yah is a contracted form of YHWH bearing all the full meaning of YHWH, but it does not delineate how this process occurs. The same source indicates that this is a poetic form used in song. A glance at the references to the 48 passages in which it occurs affirms this. What is the grammatical/linguistic process of Hebrew contractions and how specifically does YHWH contract to Yah?
It seems to me that within the Psalms, the contracted form of Yah has to do with it being a literary poetical form. Does that sound right?