Translation/i18n service for .po files with an API?

We're in the process of translating our website which uses gettext strings and .po resource files for the UI element text. We're a fairly fast-moving startup, so we frequently deploy and add new strings. So we're looking for a way to automate the process: an API where we can upload our new .po, humans translate it, then we get a callback which tells us the translated strings are ready and we make another API call to get the translated .po. Anybody know of such a service, or have any suggestions? We've looked at ICanLocalize, but its API is currently limited to documents (doesn't support strings). We've also looked at myGengo, which is very documented-oriented, and their Strings product is nice but doesn't link with the translators.