Englsh/Italian Law Dictionaries - Giuffrè editore's Dizionario Giuridico
The only English/Italian, Italian/English law dictionaries I know are Giuffrè editore's Dizionario Giuridico. There are two volumes, one is Italian/English and the other, as you might expect, is the English/Italian version.
These, literally, weighty tomes are both translation dictionaries and guides to British/American legal systems and principles. You could also say that they can act as something of a comparative law guide too.
It is slightly inaccurate to call them English/Italian, Italian/English law dictionaries, seeing as the definitions/explanations provided are mainly in Italian. This, of course, makes them highly useful for Italian lawyers, but not much use for non-Italian speaking lawyers who want to understand Italian legal terms.
However, if you are an Italian lawyer, either look around your offices for these dictionaries or buy them. The cost is around €180 for both. If you are a law student, try to find these dictionaries in your law faculty library - or convince someone in your family to buy you a copy.
PS I have both volumes.