J j

This letter is called “i lunga” and was used in the past instead of "i in some family names like “Jorio, Lojodice, Baj, Bajetta” and others, most of which still exist. Notice that in all cases it represents a consonantal "i", that is "i" preceded or followed by another vowel. It was also used in common words like "jeri, jato" ( yesterday, hyatus); these are always spelt "ieri, iato" nowadays.

In all these cases, "j" is pronounced like English "y" (and indeed the variants “Ayala, Loyodice” also exist).

In loanwords, it is usually pronounced as in the language of origin: the easiest case is German, that uses "j" like Italian - see Jung, Jungfrau, jodel...

For the rest, it depends on wether a person has at least a basic knowledge of other languages: in that case French Jacques, Spanish Maja and English James are pronounced more or less correctly.

A few decades ago, however, there were families who named their children after James Dean but called their baby something like "Yahmess" - pronouncing James as if it were an Italian word.

An important street in Milan was named after Dr Edward Jenner but the Fascist regime insisted on using Italian all over, so the plates read "Edoardo Jenner". It looks as if it were one of the surnames ending with "-er" that are common in some areas of North-eastern Italy and sure enough the local people called it "Viale Yenner". Now, even if you know that he was an English scientist, you have to say what everybody else says - or your taxi-driver won't understand where you want to go.