The question is, was this a conscious human design decision or did the algorithm learn to do that by itself?

I would believe if someone said it was completely organic. It's just how Internet is and how social graphs build up. The typical American notion that the Internet is nearly 100% dominated by American English socio-cultural platform and English is the foundational language of the world's all cognitive processing is just an annoying megalomaniac hallucination.

English is used as a lot as a fallback language for inter-cultural exchanges. In that sense it's kind of dominating, but that's it. Intra-cultural communications happens in local languages, and even if that preferred language happened to be one of en-* locales, that only means everyone is functionally bilingual, and it doesn't mean cultural informational borders don't exist. Data still only goes through bridging connections.

Considering the algorithm did not crawl out of the primordial ooze unbidden by man I am going to guess the former.

The algo learned "by itself", but humans set a objetive to optimize and then implemented it to do so as well as it they could.

So essentially both I guess?

Why is that the question? If it learned to do it by itself it still is being allowed to do it by humans.

You don't deserve the downvotes from the immature peeps around here. Your question is 100% valid.

I would lean for the latter, the simple explanation may be that people just prefer local content.