input: Write a function to implement a command-line interface for downloading subtitles for movies and TV shows. The function should accept one or more release paths as arguments and allow specifying the language and subtitle site to use. The available commands are "download", "exist", "test", "list", "help", and "version".
  
  assert download_subtitles(['/path/to/movie1', '/path/to/movie2'], ['opensubtitles', 'subscene'], 'en')==None
  assert is_subtitles_exist(['/path/to/show1'], ['addic7ed'], 'es')==None
  assert test_engines(['opensubtitles'])==None
  assert main(['--list'])==None
  assert main(['--help'])==None
  assert main(['--version'])==None
output: def download_subtitles(release_paths, subtitle_sites, language):
      pass
  
  def is_subtitles_exist(release_paths, subtitle_sites, language):
      pass
  
  def test_engines(subtitle_sites):
      pass
  
  def main(args):
      pass