Since when has "J" been sounding like [dʒ] and no longer "Y" [duplicate]
There are words that have "j" where in most languages it would be pronounced like romaji "y".
Take for example "Jesus", "Jehovah", "John". It should be pronounced "Yesus", "Yehovah", "Yohn".
Slavic languages and Esperanto have "j" sound like romaji "y" so if you'd write "Jessica", it would be pronounced "Yessica". Now, why isn't that in English? Why does also in Spanish "j" sound like "h"? How did this transformation start?
Also, why is "halelujah" not written like it's pronounced: "haleluyah"? Ironically "trojan" is not just an English word, but a Croatian word too that sounds like "troyan". Why is the "j" there if it sounds like "g" and not "y"? Why isn't "Troy" "troj"? I'm so confused! When is it "j" and when is it "y"!?
Solution 1:
The letter J in English has always been pronounced the same way since it was introduced. It replaced the Old English letters cg which had the same sound:
In English, ⟨j⟩ most commonly represents the affricate /dʒ/. In Old English the phoneme /dʒ/ was represented orthographically with ⟨cg⟩ and ⟨cȝ⟩. Under the influence of Old French, which had a similar phoneme deriving from Latin /j/, English scribes began to use ⟨i⟩ (later ⟨j⟩) to represent word-initial /dʒ/ in Old English (for example, iest and, later jest), while using ⟨dg⟩ elsewhere (for example, hedge).
The first English language book to make a clear distinction between ⟨i⟩ and ⟨j⟩ was published in 1633.
(Wikipedia)
Solution 2:
In French and Portuguese, the Latin palatal glide /j/ came to be pronounced with audible frication, /ʒ/, so that is how the letter came to be pronounced in those languages. This has also happened to /ʎ/ (written 'll') in some American varieties of Spanish.
This may have arisen in a similar way to the phenomenon in modern French, where in a word like 'oui' one can sometimes hear a fricative on the end, (though here it is unvoiced and velar /h/ rather than voiced and palatal as /ʒ/).
As Josh61 has said, English borrowed this notation from French.