instance method fetch

# File activesupport/lib/active_support/vendor/i18n-0.4.1/i18n/backend/cache.rb, line 56
        def fetch(*args, &block)
          result = I18n.cache_store.fetch(cache_key(*args), &block)
          raise result if result.is_a?(Exception)
          result = result.dup if result.frozen? rescue result
          result
        rescue MissingTranslationData => exception
          I18n.cache_store.write(cache_key(*args), exception)
          raise exception
        end