I have seem it happening. always the same users.

Probably the are navegatin in new and as soon as they see non-english they downvote. These people doesn't even have a single post in other than english,

You vastly underestimate the idiocy and childishness of Americans. I've seen people comment things like "use English, this is a US website", "go to another site for your own country if you want to use anything other than English", etc. even though the posts were in communities/subs specific for the language the post was in.
This has always been a thing online.
Many Americans are so dumb they think they are the vast majority on any website, and everything should be via their rules and ways. And there are several other things that seemingly only Americans are dumb enough to do and/or to not understand, things like timezones (even though they have several within their country), that the vast majority of the world uses Metric, that not every country has the same products or services, that their subjective experience of anything is in fact subjective, etc. I could go on for several more paragraphs with things like this.

Except not everyone has learned english, not everyone can especially older people.

Lemmy has that feature built-in that communities can support arbitrary languages. If you don't want to see them you can literally just pick your languages in your profile, and it'll automatically ignore what you can't read.

A bit weird in practice, but it's intended from the start to be available in everyone's languages without having to make news-de, news-fr, news-es communities or have to rely on regional instances.

If we went with maximizing who can read your post then it should be in Chinese. The assumption that english is the default language for everything is very american.

I mean, of course you would hate diversity. Given the history of how you treated the natives.