`Edition#translatable?` returns false unless overridden in a subclass and seems to be the main way to indicate whether or not a given subclass of edition should be translatable. In theory `Edition#available_in_multiple_languages?` should be available for all editions but it relies on the data for the edition rather than the intended behaviour.

Perhaps I should modify `Edition#available_in_multiple_languages?` to check `#translatable?` first?