Enable lazy translation

This change makes it so that if the user makes a request with an
Accept-Language header and the response is an error where the
message is translatable, then the message will be translated to
the requested language (or the most appropriate language
available).

completes bp user-locale-api

Change-Id: I5b0b02e0459a6a444baa12f8722adb829b7e152b
Merge "Enable lazy translation"