Ideally offline and either Android or Linux. Just looking to see what's out there and I didn't see much yet besides some dictionary or DIY flashcard apps
+1 for anki. I struggled for years to find anything decent for Swahili and there is more content for Swahili than I got out of Duolingo. One thing I didn't know about anki until i tried it because I didn't see anyone mention it, the flashcards can include pictures/videos/audio.
Yes. I believe all self-hosting apps are like that. As an example, I have a docker container running Searxng and I use it locally on my PC as default search engine. Just keep in mind that docker compose port mapping (e.g. "3000:80") attaches to all available IPs unless you specify it like "127.0.0.1:3000:80".