Speaking as a total ignorant from a coding perspective. But I guess that wouldn’t be the hard part, considering that most of Duolinguo is just boxes and text inputs. How difficult it is to create a database of competent linguists with an efficient training who can progressively enhance your understanding of languages?
As someone who is at around a high B2/low C1 level in Dutch now and moved to Belgium and used dualingo in the beginning I have a bit of insight into it.
It doesn’t do shit for grammar and sentence structure, but it builds vocabulary. If you learn only with dualingo, you will probably make a lot of mistakes, flipped adverbs, verbs in the wrong place, sentence structure errors, etc…
It definitely made me feel like I could speak Dutch because I could read it MUCH better after 1/2 of the dualingo course, but then when I moved, speaking was pretty bad and I had only moved up to an A2 level with the vocab of maybe B1. You definitely cannot become semi-fluent or fluent with dualingo. It doesn’t teach, it only helps practice what you have already been taught.
Conversely, I’m at a similar level in Dutch and I’d attribute a lot of my grammatical knowledge to Duolingo, especially modal verbs. However I have scoured dutchgrammar.com many a time because I learn well from reading textbooks. It hasn’t helped me at all with output though; I was quite bad at that until I moved to NL.
