input: This script provides a command-line interface for downloading subtitles for movies and TV shows. It allows users to specify one or more release paths, along with optional language and subtitle site parameters. Available commands include "download," "exist," "test," "list," "help," and "version."
  
  What is the primary function of the "download_subtitles" function in this script?
output:     
      for release_path in release_paths:
          if not os.path.exists(release_path):
              print(f"Error: The path '{release_path}' does not exist.")
              continue
          
          if os.path.isfile(release_path):
              download_subtitles_for_file(release_path, language, subtitle_site)
          elif os.path.isdir(release_path):
              for root, dirs, files in os.walk(release_path):
                  for file in files:
                      file_path = os.path.join(root, file)
                      download_subtitles_for_file(file_path, language, subtitle_site)
          else:
              print(f"Error: The path '{release_path}' is neither a file nor a directory.")
  