code: def get_strings_to_translate(self, po):
          
          strings = []
          for index, entry in enumerate(po):
              if not self.need_translate(entry):
                  continue
              strings.append(humanize_placeholders(entry.msgid))
              if entry.msgid_plural:
                  strings.append(humanize_placeholders(entry.msgid_plural))
          return strings
docs: Return list of string to translate from po file.
  
          :param po: POFile object to translate
          :type po: polib.POFile
          :return: list of string to translate
          :rtype: collections.Iterable[six.text_type]