For me Duolingo is woefully ineffective. A far better method is Pimsleur plus Anki. Ankify the Pimsleur audio, make your own Anki cards with most of your vocabulary in cloze phrases. Ankify the audio on as many of those cloze phrases as you can using native speakers. Work at it daily. Use a textbook to learn the grammar. This is a system that works. It’s the fastest way I know of to begin understanding languages intuitively. No need for mental translation. No difference in how your mind responds to “What do you want to eat?” and “你要吃什么?”

Of course, Duolingo’s valuation isn’t connected to success in learning language. It’s connected to success in convincing people that they can and should learn a language.