YouTube's localization options limit content to submissions from a particular country, and the language selection options allow users to change the interface language. This is one of those interfaces that becomes clear when you've clicked the links, because the option are hidden until you click the "Worldwide" link. Qualifying labels like "Content: World | Lang: En (US)" might make these very obvious. It's nice that YouTube gives you that content selector. I'm just not sure how this plays in other countries when there is a dual content/language choice like this. Simplest manifestation of this in most sites is just to switch languages, in which case flags are usually pretty clear.