This later spelling of the name holds the key to understanding where our use of “Jesus” in English originated, and why most English translations of the Bible render it “Joshua” in the Old Testament and “Jesus” in the New.
http://www.cogwriter.com/jesusname.htm
The Origin of the Alphabet. The original alphabet was developed by a Semitic people living in or near Egypt.* They based it on the idea developed by the Egyptians, but used their own specific symbols. It was quickly adopted by their neighbors and relatives to the east and north, the Canaanites, the Hebrews, and the Phoenicians.
http://webspace.ship.edu/cgboer/alphabet.html
It is a descendant of the letter I and was not generally considered a separate letter until the 17th century. The early history of the letter J is the same as the history of the letter I. I is a descendant of the ancient Phoenician and Hebrew letter yod and the Greek letter iota” (Vol. 10, 1992 ed.).
http://www.yaiy.org/literature/MistakenJ.html
The History of j. The letter j is rather different to those discussed so far, as it did not exist in Latin and, of course, a great deal of the medieval literate tradition is in Latin. This does need a little explanation.
http://medievalwriting.50megs.com/scripts/letters/historyj.htm
The New Book of Knowledge shows the letter I (hence the J as well) derived from the Hebrew yothe (y), which is the first letter of Yahweh’s Name (hwhy, YHWH, known as the Tetragrammaton or “four letters”; Hebrew is read from right to left). It is also the first letter of Yahshua’s Name.
http://www.yaiy.org/literature/MistakenJ.html
The Savior’s name could not begin with the letter J because it did not exist when He was born –not even a thousand years later! All good dictionaries and encyclopedias show that the letter J and its sound are of late origin. A chart on both the Hebrew and Greek alphabet is found on page 48 in this booklet. Take special note that there is no letter equivalent to J in either Hebrew or Greek even today.
http://www.yaiy.org/literature/MistakenJ.html
In a 15th century version of the Brut chronicle, written in a cursive script, the j of the word justs (meaning jousts) has developed large closed loops. The letter j can be seen to be a Johnny-come-lately of the medieval alphabet, and had not quite established itself by the end of the period we are looking at here.
http://medievalwriting.50megs.com/scripts/letters/historyj.htm
The great majority of English words beginning with j are of foreign (mostly French) origin, as ‘jaundice,’ ‘judge’”...(p.103). > Funk and Wagnall’s Encyclopedia (1979 edition), volume 14, page 94 under “J,” states: “J, the tenth letter and seventh consonant in the English alphabet.
http://www.yaiy.org/literature/MistakenJ.html
The Phoenicians spread their alphabet to other people of the Near East and Asia Minor, as well as to the Arabs, the Greeks, and the Etruscans, and as far west as present day Spain. The letters and names on the left are the ones used by the Phoenicians. The letters on the right are possible earlier versions.
http://webspace.ship.edu/cgboer/alphabet.html
In this word iaer, the letter i rather than j is used for the y sound, from a different 15th century Dutch book of hours. In modern Dutch the word is jaar. The letter j can be seen to be a Johnny-come-lately of the medieval alphabet, and had not quite established itself by the end of the period we are looking at here.
http://medievalwriting.50megs.com/scripts/letters/historyj.htm
where did letter j  originate
The letter J originated from Hebrew.