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.