Who on earth writes subtitles?

Any old bod grabbed at random off the street, apparently. It certainly doesn't appear to be a requirement that they should know the script, or pay any attention to what the people on the screen are actually saying, or have any kind of grasp of elementary general knowledge. I'm informed that the name of the man who postulated the existence of canals on Mars was Percy Valone. I look forward to the Wikipedia entry in due course.