Changed here about two years ago, as far as I remember.
Anyhow, I've never had an ad in a different language on youtube. It could be because in the US they might want to advertise it to the Spanish speaking residents instead of the English speaking?
It was in Spanish. I'm like wtf... I don't live in Mexico xD It's the USA lol...
My guess is that Youtube probably is doing this thing were they put some ads in Spanish because most of the American population is Hispanic. I don't know. I have had a similar thing happen to me, I was listening to Rammstein one time (for those of you who don't know what that is, it is a German Metal Band) and I got a ad that was in German. I think it was some sort of German Super Market. XD It makes sense how my ad was in German, cause the video was in German. But Gangnam Style is in Vietnamese I think and the ad being in Spanish.... my guess is, Youtube is stupid. XD
Seriously... I've heard that song on the radio think it's a good station then when the song is over they start talking in spanish. Happened twice. Yeah.... Seriously.....
It probably depends on the type of video too. Obviously, a video in Spanish is more likely to have Spanish ads.
Don't ask me what videos i was watching because I can't remember...but the multiple videos I watched that had Spanish ads before 'em were not Spanish videos