Earlier quoted context omitted.
...trying to cram their prepackaged square-shaped tools into a variety of circle-shaped holes. All languages are different and each requires a different approach. The first half of this is dead on. The second half is wrong. Duolingo's top languages are in the Indo-European family. (Their most learned language is English, next is Spanish.) Their techniques are perfectly adequate for gaining elementary vocabulary a bas…
No, languages are indeed different. Providing elementary grammar or vocabulary is next to useless in real conversation with natives. I highly doubt anyone is SOLELY learning English or Spanish through Duolingo. It's important to look at resources that languages provide- English and Spanish also have immense amounts of media to listen to and read, and obviously a lot of people to talk with. I would say that helps far…
My point is that a particular approach tends to work similarly well across many languages within a language family. Duolingo's method is effective at providing elementary grammar and vocabulary within Indo-European languages. I agree that it does not get you a sufficient vocabulary to read, or the verbal reflexes for speech. But it is an effective approach for an absolute beginner.
Everything that I've heard about it says that it is basically useless for various Asian languages. Even for absolute beginners. For example my wife used Duolingo with languages like Polish and Spanish. She was quite happy with the results, even though she outgrew what the app can do. However despite these good experiences it took her less than a week to decide that it was useless for Japanese, and move on to a random flashcard program instead.
As an interesting aside, we have objective evidence of these linguistic differences from machine learning. Google Translate originally worked by a form of statistical pattern matching across large numbers of original and translated documents. This worked brilliantly for Indo-European languages, but did badly for various Asian languages. To my understanding for much the same fundamental reasons that Duolingo does.