Sorry for the big off-topic. I just can’t help when it comes to etymology.

Edit: in case you missed it, the letter “I” was the Latin language character for “J” until the 4th or 5th century.

What changed around the 4th~5th centuries were sounds, not letters - the Latin words using the sound [j] (as in yes) were being pronounced with [d͡ʒ] (as in jazz). Even everyday words like iocus (game) or iam (already).

But people kept spelling them the same - you’d use “I” for [i ɪ j ʒ dʒ] (as in beet, bit, genre, jazz), and let context tell them apart. For any language using the Latin alphabet, not just Latin herself, as shown by Shakespeare:

The iniury of many a blasting houre;
Let it not tell your Iudgement I am old,

At most you’d flourish some “I” with a downwards curve, for easier reading; such as when you got 2+ “I” in a row. This mostly affects numbers (like XIII being spelled “xiij”), but also a few words like Old Spanish “fiio”=“fijo” (“son”; modern Spanish “hijo”).

Edit 2: in case you also missed it another group changed EL’s name to Allah

It’s more like both sides changed it. Without going too much into detail:

• the proto-Semitic word was around *ʔil or so
• the Biblical Hebrew pronunciation of ⟨אל⟩ was probably [ʔil] too, even if Tiberian Hebrew would read the word as [ʔe:l] “El” instead.
• Arabic “Allah” is most likely a contracted expression of [aɫiɫɫa:h]; [aɫ] is the article and the [aːh] a vocative. The underlying root is [ʔil]~[ʔill], spelled ⟨إِلّ⟩~⟨إِل⟩.