Well, surely the idea is that anyone can watch any video in any language. Especially enabling the non-English-speaking world to consume the much larger corpus of English-speaking content.
The idea is great. They just botched it at the UI level.
In practice it means clicking a video you think is in your native language but it's actually in English with low quality auto-subs, but there's no reason Youtube couldn't improve the UX here, like indicate that it's been auto-translated or let you easily filter out content that's not in your language.