Language learning in general though, I have found, is not that amenable to gamification. Some learning methods may be more efficient than others, but even with the most efficient methods, real language learning is still inherently and unavoidably a slog. So if you come across a method that makes it "easy", chances are it's not actually working. It's too easy to trick oneself to think that one is making progress, and then find oneself unable to communicate when called upon to do so.
In the polyglot (ie actual practitioners of extreme language learning) community, there are many super talented language learners but a common pattern among them is the use of surprising traditional learning methods. Most do not use Duolingo but instead elect to do things the hard way, by actually going through workbooks, talking to tutors on iTalki, making mistakes, exposing themselves to media, translating, etc. Space repetition tools are sometimes used. Pimsleur is good for speaking, but not reading/writing so it doesn't get used that much.
There are clips of YouTubers where creators show you how to learned a language to a conversational level in 24 hours etc. but if you look more closely, the experiments are highly edited and the actual outcome is not that great.
I've resigned myself to the fact that the way to actually to learn a language is to jump in and do it the hard way, rather than through easier shortcuts. Language learning is about creating new reflexes and creating new pathways int he brain and there's no easy way to do that (the brain itself resists) without discomfort.
That said, tools like Duolingo do create fun and interest in a language -- and fun is needed to sustain oneself through the journey.
Go to a foreign country and try to get laid. Genuine intrinsic motivation, and the difficulty increases with age. If nothing else, this education is good preparation for a career in business
How so?
Using a romantic partner as a language-learning partner gets old for said person after a while, especially if you're not actively making progress on the language on the side. Unless said romantic partner is a language teacher, it can be annoying for them to constantly be correcting your mistakes. Over time, this annoyance can actually harm the relationship. Also most native speakers of a language aren't always good teachers -- they may know how to use the language but usually can't explain how things work. It's better to get a tutor whose job is to instruct, bear with your mistakes, and go home after. It's easier to for someone to bear with your mistakes if they don't have to spend all their free time with you.
As for language immersion by living in a country, you'd be surprised how that doesn't really work unless you're actively learning on your own or taking classes. Case in point: I lived in a French-speaking province for 4 years but can barely speak French -- I just never bothered learning. You'd think necessity would force one to learn but there are so many ways to get around actually doing it (e.g. hanging out with expats, using gestures/hand signs, Google Translate, etc.) On the other hand, there are folks who've never been in a Francophone country who can speak French at a high level, often through active learning. In fact, many polyglots often become fluent in a language without ever setting foot in the language's country of origin.
The key really is putting in the work. Getting laid in a foreign country may help kickstart the process, but to achieve working fluency, there are no real shortcuts.
(well, there is one, which is that you already know a related language. This is the only major accelerant. You can learn Afrikaans very quickly if you speak Dutch. Similarly for Malay -> Indonesian, Portuguese -> Spanish ... interestingly, this pair is asymmetric: Spanish -> Portuguese is harder than vice-versa)
What Duolingo has been best for is getting a baseline vocab and familiarity with the language. It also lets you stay fresh/keep making progress when you don't have time or mental effort to spend more than a few minutes a day.
This isn't as big of a problem for latin based languages (English native) however.
I’ve tested Duolinguo for languages I want to learn, for some I already know and a language BA/MA holder I can guarantee that Duolingo is total crap. This is just a feel good app. Just like another post was mentioning hiw note taking can do more harm than good because it feels like work, Duolingo is given the user the feeling of work and progression while very very little knowledge is gained. Let’s take Japanese as an example. Hiragana and katakana are each divided in 4 parts: a user can easily spend weeks on that and feel he’s making progress. University student on the other side learn that in a week... (for slow learners)
I took French in middle/high school with the standard lecture/hw school structure and was a lot less successful than I've been with Duolingo. Duolingo alone probably isn't enough to really learn a language but combined with other resources it provides a great structure to keep you committed and provides a great foundation to build from.