rails--rails/actionpack/lib/action_view/helpers/translation_helper.rb

require 'action_view/helpers/tag_helper'

module ActionView
  module Helpers
    module TranslationHelper
      # Delegates to I18n#translate but also performs two additional functions. First, it'll catch MissingTranslationData exceptions 
      # and turn them into inline spans that contains the missing key, such that you can see in a view what is missing where.
      #
      # Second, it'll scope the key by the current partial if the key starts with a period. So if you call translate(".foo") from the
      # people/index.html.erb template, you'll actually be calling I18n.translate("people.index.foo"). This makes it less repetitive
      # to translate many keys within the same partials and gives you a simple framework for scoping them consistently. If you don't
      # prepend the key with a period, nothing is converted.
      def translate(key, options = {})
        options[:raise] = true
        I18n.translate(scope_key_by_partial(key), options)
      rescue I18n::MissingTranslationData => e
        keys = I18n.send(:normalize_translation_keys, e.locale, e.key, e.options[:scope])
        content_tag('span', keys.join(', '), :class => 'translation_missing')
      end
      alias :t :translate

      # Delegates to I18n.localize with no additional functionality.
      def localize(*args)
        I18n.localize *args
      end
      alias :l :localize


      private
        def scope_key_by_partial(key)
          if key.to_s.first == "."
            template.path_without_format_and_extension.gsub(%r{/_?}, ".") + key.to_s
          else
            key
          end
        end
    end
  end
end