# File lib/gettext_i18n_rails/ruby_gettext_extractor.rb, line 67
    def extract_key_plural(args, separator)
      # this could be n_("aaa", "aaa plural", @retireitems.length)
      # s(s(:str, "aaa"),
      #   s(:str, "aaa plural"),
      #   s(:call, s(:ivar, :@retireitems), :length))
      # all strings arguments are extracted and joined with \004 or \000
      arguments = args[0..(-2)]

      res = []
      arguments.each do |a|
        next unless a.kind_of? Sexp
        str = extract_string(a)
        res << str if str
      end

      key = res.empty? ? nil : res.join(separator)

      return nil unless key
      key.gsub("\n", '\n').gsub("\t", '\t').gsub("\0", '\0')
    end