Extracted from The Institute of Translation & Interpreting (UK) website:
“What is the purpose?
What do you want to do with your translation? It sounds like a very basic question, but it is one worth asking as it could help you to save money!
For example, if you have a sales brochure that you want to translate so that it can be used at a trade fair abroad, you will need a translator who can write good copy in the target language and who will be able to advise on aspects such as the use of images. On the other hand, if you want to tender for a contract issued by a foreign organisation, you will need a translator with strong legal skills and an understanding of the technical aspects of your industry. Or perhaps a web search has just unearthed a mention of your company or product in a small regional newspaper that you have never even heard of – you simply need to find out what it is the journalist is saying about you. Whatever it is you need from your translation, you should tell your translator before giving them the job.
When it comes to interpreting, the purpose is just as important. If you are organising a conference for a group of people with a range of different languages, you will generally need a pair of conference interpreters for each language combination. Alternatively, if you are hosting a visit to your factory by a customer based abroad, you will need a business interpreter who is fluent in both your and your customer’s languages, and is knowledgeable about your industry. Finally, if you find yourself in need of assistance in court or other parts of the justice system, you will need a Police and Court Interpreter who not only knows the languages and vocabulary of the legal system perfectly, but also understands the processes and conventions involved.
“For non-linguists, the process of buying translation and interpreting services can often be difficult to negotiate. This section aims to help you find your way.”
Read the whole text here: http://www.iti.org.uk/about-industry/advice-buyers
Or see here the publication “Getting it right “ – English