Pretty much every day at work I make use of Japanese Law Translation, which is pretty much what it sounds like it is, but it's got a few neat tricks up its sleeve.
The website is maintained by the Japanese Ministry of Justice, with contributions from various lawyers (including those at my firm), legal academics, and others (more about its genesis is available here). It is in effect the official translation of legal terms in Japanese.
It has a basic bilingual dictionary, where you can look up words in English or Japanese. (And there are rumblings of later expanding it to include Chinese, Spanish, and Portuguese as well.) It then gives you a list of the definitions that contain the word plus links to the laws it's found in.
However, not all terms that have been translated can be found in the dictionary, so another very useful tool is the ability to search translations of the law for the word you're looking for. That will get you both the English and the Japanese text and you can figure out how the word was translated.
As the website is a work in progress (and will need regular updating as laws change), not all laws and regulations are included yet, and as mentioned above not all terms have been added to the dictionary, but it is a very useful tool if you ever have a need for legalese in Japanese.