The American Translator’s Association has a great guide for buying translations called “Translation: Getting it Right“. This is a must-read for anyone who needs a translation done and is unfamiliar with the world of requesting translations.
One component of requesting translations that is very important is the context around a document. Translation cannot be done with only the document to translate and no other information; a lot of things external to a document affect how it is translated. For example, one important thing to know is if the translation is being done “for information” or “for publication”. Someone might want a “for information” translation if they only want to understand a document, but it doesn’t have to have perfect style because it’s not going to be published.
Another case is that the person who needs a translation might need it to be done for a different audience than the original. This means the style, register, and other aspects of the language will be different than if the audience was the same as the original. This audience question is very important and can result in very different translations; there is absolutely not one “correct” translation for any particular document. Think about it in terms of original-language writing: if someone asks you to explain how a new phone works, then you need to know if you’re explaining it to – a five year old, a technology-savvy college student, or an elderly person who hasn’t used very much technology. You will use very different words, different analogies, and convey different levels of information.
So overall, that means a translation request isn’t complete if it only contains the document to translate – it needs the context too.