input: Write a function to provide a command-line interface for downloading subtitles for movies and TV shows. The function should support various commands such as "download", "exist", "test", "list", "help", and "version". It should also allow specifying the subtitle language and site. Implement the main functionality to handle these commands and provide appropriate outputs.
  
  assert main({'download': True, '<releases_path>': ['path/to/movie'], '--engine': ['opensubtitles'], '--lang': 'en'}) == None
  assert main({'exist': True, '<releases_path>': ['path/to/show'], '--engine': ['subscene'], '--lang': 'fr'}) == None
  assert main({'test': True, '<engines>': ['subtitle_club']}) == None
  assert main({'--list': True}) == None
  assert main({'--help': True}) == None
  assert main({'--version': True}) == None
output: def main(args):
      if args.get('download'):
          releases_path = args['<releases_path>'][0]
          engine = args['--engine'][0]
          lang = args['--lang']
          # Implement download functionality here
          pass
      elif args.get('exist'):
          releases_path = args['<releases_path>'][0]
          engine = args['--engine'][0]
          lang = args['--lang']
          # Implement exist functionality here
          pass
      elif args.get('test'):
          engines = args['<engines>']
          # Implement test functionality here
          pass
      elif args.get('--list'):
          # Implement list functionality here
          pass
      elif args.get('--help'):
          # Implement help functionality here
          pass
      elif args.get('--version'):
          # Implement version functionality here
          pass
      else:
          # Handle unknown command
          pass