Can't I add some kind of string to the URL of the video to make it start off with the subtitles on and in the "right" language?
We do have the option to have the video start up from a particular time, so why not subtitles too?
And, Google Translate does add those strings to the URL (e.g. http://translate.google.com/#en|nl|), so I don't understand why the same is not automatically happening on YouTube too.