History of the Letter J
I'm stalling on translating about the letter "j" because its origin in English is not likely the same story in Spanish.
In a nutshell, in the English language, the letter J did not come into existence until the 1600s. And it was really an I with a tail on it. While that's true for English, what would the case be in Spanish?
1 Answer
This is from the Wikipedia article on "j".
In the Romance languages J has generally developed from its original palatal approximant value in Latin to some kind of fricative. In French, Portuguese, Catalan, and Romanian it has been fronted to the postalveolar fricative /?/ (like s in English measure). In Spanish, by contrast, it has been both devoiced and backed from an earlier /?/ to a present-day /x ~ h/,[7] with the actual phonetic realization depending on the speaker's dialect.
I am no phoneticist, but the gist of the article is that the English and Spanish "j" both derived indirectly from Latin. I have found references that implied that it came from Arabic, but most of the resources agree on the Latin derivation.