Failing feature for non-English world news
Editions now have a primary locale

So we can differentiate between a normal (English) edition and
non-English ones, we store a "primary locale". By default, this
is English, so existing documents should behave as before.
Edition translations fallback to a primary locale

globalize3 uses globalize_fallbacks when checking translated attribute
values. By default, it checks the current locale before falling back
to whatever the default locale is. By overriding globalize_fallbacks
we can have editions fallback to their primary locale, rather than the
default one, meaning that non-English editions still return values
(i.e. are valid) when loaded in the default English locale.
Non-English editions do not get a slug

Because we cannot reliably generate readable slug strings from UTF-8
foreign languages titles, Documents belonging to non-English
are saved without a slug, meaning they fallback to their id for
identification.
Re-organise model code for non-English editions

Rather than stuffing the code directly in the Edition model, try and
keep it local to the appropriate concern.