(use first default key that resolves to a translation). this might, depending
on the backend implementation save some expensive lookups (like db lookups)
client libraries to the backend: clients now can pass a block to
backend#populate which can contain code to load and register translations.
This makes sense for backends that persist their translations (e.g. to db)
so the repeated loading and passing of translations throughout the server
startup would be wasted resources.
Joshua Peek