def available_locales_set #:nodoc:
      @@available_locales_set ||= available_locales.inject(Set.new) do |set, locale|
        set << locale.to_s << locale.to_sym
      end
    end
def available_locales_set #:nodoc:
      @@available_locales_set ||= available_locales.inject(Set.new) do |set, locale|
        set << locale.to_s << locale.to_sym
      end
    end
Caches the available locales list as both strings and symbols in a Set, so
 that we can have faster lookups to do the available locales enforce check.