For non-linguists, buying translations is often a source of frustration. In order to spare you this frustration, I am offering you this guide to get it right, which has been published by a group of translator and interpreter associations.
It deals with questions that should be answered before ordering a translation and advice that is worth following:

• Does it really need to be translated?
• A picture is worth a thousand words
• Think international from the start
• How much will it cost?
• How important is style?
• Resist the temptation to do it yourself
• Finalise your text before starting the translation
• What about machine translation?
• Tell the translator what it’s for
• Teachers & academics: at your peril
• Professional translators work into their native language
• What language do your readers speak?
• An inquisitive translator is good news
• The more technical your subject, the more important it is that your translators know it inside out
• The home stretch: have typeset copy proofread by your translator
• Typographical conventions vary from one language to the next
• Translators and bilinguals: look closer
• “Technical terms pose few translation problems” A widely-held myth.
• Choosing a supplier
• Get involved

Taken from: Translation getting it right – A guide to buying translations by Chris Durban