t_scope.rb

module I18n
  # Usage (Haml in examples):
  #
  #   - t_scope(:"public.sign_up_or_log_in") do |s|
  #     = simple_format(s.t(:text,
  #       sign_up: link_to(s.t(:sign_up), signup_path),
  #       log_in: link_to(s.t(:log_in), login_path)))
  #
  # is equivalent to
  #
  #   = simple_format(t(:"public.sign_up_or_log_in.text",
  #     sign_up: link_to(t(:"public.sign_up_or_log_in.sign_up"), signup_path),
  #     log_in: link_to(t(:"public.sign_up_or_log_in.log_in"), login_path)))
  #
  # Note that you need to use "-" or it will render the string twice.
  #
  def self.t_scope(scope)
    t_scoped_class = Struct.new(:scope) do
      def t(key, opts = {})
        I18n.t(key, opts.merge(scope: scope))
      end
    end

    yield t_scoped_class.new(scope)
  end
end

t_scope_spec.rb

describe I18n, ".t_scope(scope)" do
  it "provides a scoping object" do
    I18n.backend.store_translations(I18n.locale, {
      foo: {
        text: "Hello %{world}!",
        world: "world"
      }
    })

    I18n.t_scope(:foo) { |s| s.t(:text, world: s.t(:world)) }.should == "Hello world!"
  end
end