PhD research: translating non-English documents into English


Hey guys,

For my research, I will be working with a number of non-English languages (including some I do not personally understand). In these circumstances is it better, do you think, to limit my sample size to only those languages I understand OR to employ translation services and include a relevant disclaimer in my research concerning translation?

Any assistance would be welcome (links to articles or texts that address this would be most welcome).