For multi-language websites, it usually gets difficult to manage the translations if the website is updated frequently and/or there are multiple translators.
String is a totally free and web-based platform for managing the language files of multi-language websites.
It enables you to import languages files (almost in any format) or start a project from scratch and start translating the strings.
You can invite any number of users and let them help you with the translation process by controlling the user-based read/write permissions.
Once the translation is complete, simply export the language-files (PHP -array, define-, Yaml, .INI, .strings -for iPhone-, Po) and that's all.
The application has a very easy-to-use interface with features like "the ability to see revisions" or "commenting for each string" and much more.