If you're doing an iOS app, here are some other options:
These are specifically built to handle the translation of iOS development file formats. I don't know for sure, but I believe most services probably use Gengo.com as their actual translation back end. I've used Gengo directly before. While it's hard for me to say if the translations were accurate, I do know that translators have come back to me with helpful insight when using the Ultra service, and they have been communicative when I had questions using the Pro service.