Unsystematic app will take years to learn a perfect langauge. Every language starts with Vocabulary, Grammar, Tenses, Degrees of comparison, Direct Indirect speech and so on. DUOLINGO starts abruptly from anywhere and ends up nowhere. I have seen many users learning since 1000 days and still learning and still going on to learn. I was an IELTS faculty so I know the above procedure make someone learn. Duo is just a translator with fix programme.