Tip for you since it sounds you are genuinely trying it out but are running into issues: you can post and comment on outside Lemmy communities without creating a different account for the most part. Just navigate to lemmy.world/c/[community name]@[other site domain]. Example: https://lemmy.world/c/[email protected] means you can interact with the community on mander.xyz while staying on your lemmy.world account.
A Lemmy server agnostic link can be made in the form of ![community name]@[other site domain]. Example: [email protected], or [email protected] to help people from anywhere on lemmy to link to c/fediverse.
There’s still a lot of gaps like official methods to redirect post and comment links to your instance (I heard it was coming soon) It is indeed behind Reddit in a lot of technical and social aspects, but I think it’s not completely a bad thing.
The English + Undefined issue is indeed a nasty issue that makes half of the content disappear for a reason that’s not easy to figure out. It really should be a separate checkbox of whether to show or hide posts where the language is not labelled. I do think that Undefined is selected by default now, but might still get unselected if the language setting is clicked and changed.
For those people saying “Ctrl+Click, should be obvious”, that won’t work at all on mobile web UI.