I'd like to block entire instances like the ones where I can't read the language, but I can only block individual communities. Nothing against other languages, and I could stand to expand my scope from 3 languages, but seeing 6 posts flood my feed in a language I can't even identify is a bit uncomfortable
Do you have the languages you know selected in your user settings page? There's a panel on the left side where you can click on the entries. After clicking on the first one, you can hold Ctrl for subsequent clicks to make multiple selections before saving your changes.