We've been using angular-gettext[1] along with Transifex and it's made a significant impact our development and translation management.
1. You never will run out of keys.
2. Makes code much easier to read with a real language on messages instead of keys that can't possibly describe the whole message.
3. While writing code, you don't need to stop to think in a new key to add your message, go to the key->value list file and add it there. You just wrap you message with _('') and it's done.
4. Easier to write messages that have variables inside using sprintf or similar.
The only benefit I can see is when you want to change the English version you can do so without breaking the relationship.
Just see my comments above :) If angular-translate doesn't fit to your needs, that's okay. Just stick with angular-gettext. But you'll lose all the awesomeness like async loading, fallback languages, language negotiation etc..
But I mention here, that we also see how we can bring such kinda support. Like using english texts as translation ids.