I agree regarding the time needed, but it's not clear to me that the Duolingo way would really lead to proficiency, even if one would invest all the time in the world.
Over the last couple of years, I've invested some serious time into learning Portuguese, first in Duolingo and then in an actual classroom. Duolingo was definitely helpful for reading proficiency, but did almost nothing for my conversation skills (let alone pronunciation). The real classes helped with the conversation skills, though I ended up supplementing them with a spaced repetition app for vocabulary drilling. Grammar is still lacking.
Another Duolingo language that I've spent quite a bit of time on is Yiddish, and I find that I can now read it quite well — but only in the exact font the app is using. I'm not entertaining much hope of ever being able to write or speak it.
Over the last couple of years, I've invested some serious time into learning Portuguese, first in Duolingo and then in an actual classroom. Duolingo was definitely helpful for reading proficiency, but did almost nothing for my conversation skills (let alone pronunciation). The real classes helped with the conversation skills, though I ended up supplementing them with a spaced repetition app for vocabulary drilling. Grammar is still lacking.
Another Duolingo language that I've spent quite a bit of time on is Yiddish, and I find that I can now read it quite well — but only in the exact font the app is using. I'm not entertaining much hope of ever being able to write or speak it.