“Mother-of-all” might be an overstatement, as I’m sure there are other thick books out there on how to draft contracts in English, but this one is very thorough:
A Manual of Style for Contract Drafting by Kenneth A. Adams
In my experience, you can find two types of books on legal writing and contract drafting: those with a textbook price tag (€50 – €100) and those with a standard non-fiction price tag (€5 – €20). This one fits into the first category but it’s probably worth it, even for translators. It really does go into far more detail than some of the other, still good, books you can find on legal writing and similar for the lower price tag.
I should acknowledge, though, before I go on and talk about the book too much, that I’ve only had it a little while and have done little more than skim through it and use it as a reference guide on occasions. In any case, while there are sections I will definitely read through at some stage, it is more a reference book anyway.
So, what’s in the book for translators? Apart from setting out, in detail, how to draft a contract and looking at most of the decisions you have to make along the way, it covers general considerations and principles on contract language and also offers a long list of terms and expressions often seen in contracts.
While you might argue that translators don’t need to know that much about how to draft a contract as they will always have a model to follow, I think most would find the considerations and discussion on language relevant and the list of commonly used contract terms useful as a reference guide for deciding whether such and such a term really does match up with what you’re trying to render in a translation.
However, I’d argue it is useful to know how contracts should and could be drafted in English. In fact — with just about any kind of translation I can think of, not just contracts — I’d say best practice would never involve just automatically replicating the structure of the source document.
Then, of course, there’s the question of where this advice sits on the continuum of contract drafting and legal English in general.
The author is from the US, so this is something to take into account, although distinctions do seem to be made between different variants of English where relevant. Apart from that, Ken Adam’s advice, as you can see from his blog, is very practical and always seeks out the clearest and most effective language and solutions. It can veer somewhat from traditional legal style, but, while clearly aiming to get rid of deadwood, it doesn’t do away with anything seen as necessary just because it might be complicated or technical. Not quite the plain English agenda but tending in that direction when it suits.
Anyway, I think a lot of the advice on language is applicable or at least useful-to-consider for translators. Although it’s probably important to keep in mind that this style may not be deemed by everyone in the industry as a standard, traditional or maybe even a “safe” approach. “Safe”, at least, from a translator’s perspective, who far more often has to play the role of imitator rather than innovator.