* English shouldn't fallback to any other locale
* Calculate fallback for default locale if it isn't English (useful for en_US)
* Reuse the fallback locale list when outputting translations to JavaScript
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
Gerhard Schlager
Sam Saffron