There is one simple condition: the original translator must have been a qualified native speaker of the target language of the translation.

If you are an agency or end-user who wishes to use review or back-translation as part of an established quality assurance program, I'll be happy to undertake the work for you, provided the original translator was a qualified native speaker. If, however, you have contracted with a person who is not a native speaker of the target language of the translation in hopes of cutting your costs, I regret that I will not undertake any review or editing of the project. I believe very strongly that in the case of written translations, the best -- indeed the only -- choice for the translator is a person who is both skilled in translation and a native speaker of the target language.

If you feel that the material is "just too specialized" and could not be read by someone without years of experience in the field, I would urge you to try to collect a specialized glossary or list of terms to facilitate the translation by a native English speaking translator, rather than wasting time and money to produce a substandard document in English which will need to be re-translated in any event.