There are two common fallacies for beginning translators and laypersons: One is that each source language term has an exact equivalent in the target language, it and the other is that bilingual dictionaries have the last word (No pun intended.) in translation. The harsh truth is that neither belief holds water in the day-to-day chore of legal translation.
Before leaving you with a link to an excellent article on researching legal documents, I will say this: Spanish and English, not to mention Latin American (or Spanish) legal systems and US (or British) legal systems, are two different entities with a life of their own.
Therefore, we cannot treat the process of translation as it we were putting together pieces of the same linguistic jigsaw puzzle. In fact, many times we are faced with devising an new text in the target language that reflects the original meaning. In order to do so, translator Madeline Newman Ríos stresses the need to research the original legal provisions mentioned in the source text. By understanding a particular article or provision, it is easier to understand the way a judge or other lawmaker worded a particular sentence as opposed to plugging in a definition from a bilingual dictionary without any context.
You can read the entire PDF document, Researching Legal Translations: The Whys and Hows here.