A browser extension that progressively immerses you in a language.
Great tool for learning vocabulary while browsing reddit, or any other site! It can be a little buggy on some sites in the current state, but it's easy to whitelist or blacklist sites as needed. Because of how it works, it doesn't always teach correct grammar or sentence structure. But if you're strictly trying to build vocabulary, and keep that caveat in mind, it's quite effective.
https://berezin.io
jzlong666
https://vocabexpander.com
https://jasper.ai
https://fastscroll.io