When translating a contract, it can be surprisingly difficult to work out what to call it in English. You’d think that would be easy part!
One reason this happens is that Spanish law more tightly regulates the structure and content of certain types of contracts, which often leads to some long, exact and convoluted titles. For instance, this happens a lot with employment contracts.
In these cases, the best thing to do is usually to translate the title fairly transparently (literally) and then stick “Agreement” on the end. “Agreement” is the best default term to use because that’s what contracts are most often called in English.
Of course, sometimes they go by other names (e.g., “contract”, “form” or something else). So you must always check for equivalents. Sometimes this is the difficult part in translating the title: you know there must be an equivalent in English but can’t find it.
One way to check for the titles of equivalent contracts in English is to Google “legal form books”, which returns you links with lots of examples of contract names in English, e.g.: http://www.lectlaw.com/form.html. (I found this search tip here.)
However, in general, when trying to translate some of the more convoluted name for specific contracts, a good rule of thumb is to just go for “agreement”. You won’t find exact equivalents for many of these types of contracts, so don’t bother trying.
Alvarado, I., (2004) Guía para la traducción de contratos de arrendamiento. Master’s dissertation Universidad Nacional. Available in PDF here