code: def stem_plural_word(self, plural):
          
          matches = re.match(r'^(.*)-(.*)$', plural)
          #translated from PHP conditional check:
          #if (!isset($words[1]) || !isset($words[2]))
          if not matches:
              return plural
          words = [matches.group(1), matches.group(2)]
  
          #malaikat-malaikat-nya -> malaikat malaikat-nya
          suffix = words[1]
          suffixes = ['ku', 'mu', 'nya', 'lah', 'kah', 'tah', 'pun']
          matches = re.match(r'^(.*)-(.*)$', words[0])
          if suffix in suffixes and matches:
              words[0] = matches.group(1)
              words[1] = matches.group(2) + '-' + suffix
  
          #berbalas-balasan -> balas
          rootWord1 = self.stem_singular_word(words[0])
          rootWord2 = self.stem_singular_word(words[1])
  
          #meniru-nirukan -> tiru
          if not self.dictionary.contains(words[1]) and rootWord2 == words[1]:
              rootWord2 = self.stem_singular_word('me' + words[1])
  
          if rootWord1 == rootWord2:
              return rootWord1
          else:
              return plural
docs: Stem a plural word to its common stem form.
          Asian J. (2007) "Effective Techniques for Indonesian Text Retrieval" page 76-77.
  
          @link   http://researchbank.rmit.edu.au/eserv/rmit:6312/Asian.pdf