Please make sure you have “undetermined” selected in your list of spoken languages in your lemmy settings in addition to any other languages you speak.
Most lemmy content does not come through with a language tag, and you need to have undermined selected as an option to see that content.
A “gotcha” I just discovered: even though the selector uses radio buttons (which usually means you can only choose one), this is a multi-select list. So if you don’t also choose English (and/or other languages you understand), you’ll miss content that does have a language tag.
Designing UI ain’t easy.
This was my issue! I thought I could only pick one. Now I have both undetermined and english and I can see posts! Hooray!