Which particular legal field, they each have their own specialist vocabulary. It will probably be best to get a dictionary but it must be specific to the English speaking country you are interested in, there will be many common definitions but not all of them. https://bookauthority.org/books/best-law-terminology-books

Quite frankly, the Anglo-American legal system is so different from the Continental European one that you can learn a great deal simply from common encyclopedias in your library (or, I assume, Wikipedia). Even if you are already familiar with the basic concepts, the shelves of a university library would still be a good starting point. Considering that there are excellent German lexicons of legal terms with explanations, I'm sure there are some in English as well. If that's not enough, I'd go to a translation website such as linguee or glosbe, enter a legal term that interests me in, say, Russian, and look for all possible English equivalents and look those up with Google, hopefully ending up with a bigger or smaller number of pages with explanations and usage examples.

"Black's Law Dictionary" is the standard legal dictionary in the US. Because we got our legal system from the UK, there's going to be a lot of overlap - but there are some key differences. Is there something specific you're looking for?

Hi Sasha, When I studied law some years ago, I used "Osborn's Concise Law Dictionary" by John Burke published in London by Sweet & Maxwell.

Hi Sasha. International Legal English, by Cambridge