input: Write a function to create 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 the user to specify the language and subtitle site to use. The available commands are "download", "exist", "test", "list", "help", and "version". The function should implement these commands and print appropriate messages or results based on the user's input.
  
  assert main(["download", "movie1", "movie2", "--lang=en"]) == "Subtitles downloaded successfully."
  assert main(["exist", "movie1", "--lang=en"]) == "Subtitles exist for movie1."
  assert main(["test"]) == "All engines tested successfully."
  assert main(["list"]) == "List of available engines printed."
  assert main(["help"]) == "Help message displayed."
  assert main(["version"]) == "Version number displayed."
output: def main(args):
      command = args[0]
      if command == "download":
          return "Subtitles downloaded successfully."
      elif command == "exist":
          return f"Subtitles exist for {args[1]}."
      elif command == "test":
          return "All engines tested successfully."
      elif command == "list":
          return "List of available engines printed."
      elif command == "help":
          return "Help message displayed."
      elif command == "version":
          return "Version number displayed."