I see duolingo as a kind of modern equivalent to the language textbooks we had in school. You aren't going to seriously learn a language using it, but it gives

I see duolingo as a kind of modern equivalent to the language textbooks we had in school. You aren't going to seriously learn a language using it, but it gives you enough of a taste that you might be motivated to decide to pick up a language after using it. I do think that using duolingo too long is an inefficient way to learn a language even at beginner level, I wouldn't use it for more than a few weeks before graduating to a SRS like Anki. For intermediate to advanced I really love clozemaster. It's especially good for learning grammar, you probably want to supplement it with some pure vocabulary in an SRS.