Were I to guess, the "J" would come from the German "Jesu" ("Yay-su"), and they didn't transliterate it to "Y" when they brought the name into olde English. Or maybe "Y" didn't exist then. English picked up influences from all over Europe.
Check the Septuagint versions of the OT. It's available on Blue Letter Bible now. Joshua was transliterated to "Ἰησοῦς", and the NT writers picked it up. Greek doesn't have the "sh" sound, so sigma is as close as the Septuagint writers could get, but where did the ending "s" come from?
What I'm REALLY annoyed at is how "Iakob" (Jacob) got translated to "James" in the NT, except where specifically referring to the Patriarch. I heard that the translators of the King James Bible were trying to kiss the, er, curry favor with their patron. I don't know if that's historically documented, or just scurrilous.
As long as He answers when I pray in Jesus's name, I'm not going to get hung up on it.
The thing is if you research it, you will find more than one explaination of why it happened. And there are some that blame the Septuagint but that is not why the error occurred. Again "Ἰησοῦς" is not a name. It is a description, that is why you can look all through the Greco-Roman history and not find a Greek person named Ἰησοῦς.
There is no reason to run it through the Septuagint to explain it or the language mills, all that is, is a decoy from the truth. The word Jesus does not have anything to do with the Septuagint. The explanations up front are all lies, you have to dig deeper into the linguistics and the history. The history of the word Jesus does not go back that far. The word Jesus did not appear in The Tyndale Bible 1532....The Geneva Bible 1560.....nor the original King James Version 1611. All used the Vulgate name of Yeshua...Iesus--Iēsūs because these translations relied heavily on the Vulgate and the textus receptus, but ignored Christ's actual name.
Some of it is just a matter of turning the brain on....people do not think about what is being dumped in their lap. Miriam did not name her Son with a Greek or Latin name! Come on! Brain on! Why would people think that? Christ's name is Hebrew...יהושוע...
Pronounce Yeshua....spelt יהושוע and when it came out Miriam's lips it sounded like e-Yeshua...and Yeshua can be spelt in English. See the word? To be most accurate you have to add an e tang to the Y....eYeshua. The Strong's Exhaustive Concordance pronounces it ... ee-ay-sooce which an attempt to pronounce Ἰησοῦς not יהושוע. Look up how to pronounce יהושוע...it is not that hard or complicated.
You can spell Yeshua, you can read Yeshua, you can say Yeshua, Just as well as Christ's mother....Same thing for Yahweh. And Yeshua is the only name that can be called upon for salvation....will any name due? We are going to hope so.
Those that dealt with the scripture translations had a real desire to mess with the names....not just one person, not at any one time. At one time Yahweh's actual name was in the Old Testament nearly 6,000 times. Then it was replaced with the tetragrammaton....then it was completely removed and replaced with a description....God or Lord....just like Christ's name....not a name. Christian Bibles without the name of God the Father or God the Son in them. What does that do to the power of the scriptures? Who would want to remove the names of God the Father and God the Son from the scriptures....?
Some are trying to put God the Father's name and God the Son's name back into the scriptures but that can be difficult because in some scriptures Yahweh had regional names that started with el.
Is there power in the names of God the Father and God the Son? Are they important? I guess that is an opinion?