If you decide you want to handle a case by yourself, and I by no means suggest it, you will get bogged down in legalese. Well, while not quite a dictionary, Party of the First Part by Adam Freedman, does give you the history of legal terms and then explains them in plain English.
I just finished reading my copy and really enjoyed the book. I highly recommend this book for anyone who is thinking about the law, handling a case or has any interest in legal terminology.