Linguan

Linguan greatly simplifies localizing your Mac and iOS apps. It gives you an intelligent editor for all strings files contained in your Xcode project.
Open, edit and save XLIFF files directly (useful now that Xcode can export XLIFF files)
You get warned about duplicate tokens or missing translations. Then you can export and e-mail all missing tokens for a specific language to your translator, who can also use Linguan for filling in the translations or use his text editor of choice.
When you get the translators results back Linguan automatically merges the results into your project, even if the tokens originated from multiple different strings files.
Linguan is the most fun way to clean up your translations.
This app was created by people who are using it every day to localize their apps: Peer Assembly, BytePoets and Cocoanetics.