I've never been exposed to non-US content on Bluesky unlike Mastodon where it's a melting pot from every possible niche and location.
To me it seems like Mastodon's focus on hashtags as discovery mechanism won hard in this space thus allowing such diverse communities to thrive on the platform.
There's an implicit language filter around your default language. It was implemented because the Japanese is comparatively as large as the English audience and a lot of English language users were complaining about searches and feeds being filled by Japanese posts. I chat a lot with Japanese Bluesky because I'm fluent in Japanese; probably 50% of my Bluesky activity is with Japanese Bluesky. I've made friends with a Japanese tech reporter and they share their articles with me occasionally, so it's fun to see a non-English speaking perspective.
Unfortunately I think a lot of the people who use Mastodon and are trying to dunk on Bluesky are doing so in bad faith or not quite bad faith but a non-willingness to explore Bluesky with the same openness and curiosity as Mastodon (this may purely be from a time perspective, I mean we're all human and only have so much time to devote to internet shitposting.) I used and stopped using Mastodon before the whole Xitter thing, because I had 2 instances shutdown on me for various reasons and didn't want to bother trying again. I'm mostly on Bluesky and it seems to have the same features as Mastodon sans the easy to build instances because ATProto is a more complicated protocol. I find the network of Bluesky (or at least my feed) to be a lot less tech focused and for me this is a win. I already engage with tech people on HN, parts of Reddit, and Discord. I don't need yet another tech site full of the common tech tropes like ranting emotionally into the void or getting hung up on niche things that only tech people care about. Just my $0.02.
The feedback about not cross-pollinating non-English-speakers is good though and I've been working on a feed that uses some ML to generate cross-cultural feeds around certain topics. It's been slow going because work has been tough and I'm locked in wedding "hell" in my personal life.
To me it seems like Mastodon's focus on hashtags as discovery mechanism won hard in this space thus allowing such diverse communities to thrive on the platform.