I raised that point at Facebook when I joined (I had lived in Finland soon prior and didn’t speak a word of that terrifying language). My back-of-the-SQL estimate was several percentage points of ads were shown to someone who couldn‘t understand them.

It took six months for the company to ask someone to investigate further; he confirmed my estimation and had “the most impact anyone junior had within two months of joining the company”.

But isn't the problem the person who ordered the ads? If they pick a geographic region, but not a language, then don't those ads make sense?

Pick an IP block via APNIC, e.g. one allocated to Indonesia, and hit everything using those IPs with certain kinds of ads in the local language.

If they hit a couple of lone gringos and other ex-pats, whatever; the point is a wide net. Targeting you specifically isn't worth the trouble until your net worth is measured in 5MM or more, me thinks.

That isn’t what’s important.

What’s important is that YouTube had another user to show ads to thereby inflating their metrics so they can sell more ads at a higher price.

Ads aren’t about you, they’re about convincing marketing departments to spend more money on more ads at a higher price.