I think that it's important to acknowledge that an effective language learning approach is multi-faceted and learner-specific. Any single app can only be a small part of a larger learning strategy, combined with books or podcasts or tutors or reading and listening practice or making friends with native speakers... you need it all.

Full Disclosure: one of the developers of Japanese Complete here. We are aiming at providing learners with a full path to native-level comprehension and fluency. We estimate it'll take ambitious learners 3-5 years to complete everything. You can subscribe monthly. https://learnjapanese.best has more information

There are lots of other general language learning apps, but they’re all about the same as Duolingo. However, more specific apps can be a very useful tool. Specifically, using a spaced repetition software is the best way to memorize vocabulary. I personally use Mnemosyne, which is open source, but there’s also Anki, Memrise, and a number of others.

Pimsleur is what you want and you can get it free form your library. You can play the audio tracks from your phone if you burn the CDs. It could well be a native app, and I wish it was, but there must not be a lot of tech product vision at the Simon&Shuster.

I love Duolingo and think it's great. I took two languages in school and another for a job and I've learned more with Duolingo than with formal education. I think if you're a certain kind of nerd then learning from a textbook works great but for me the casual little lessons in Duolingo are just right. I know two sets of linguist parents and they think it's great and have their kids on it.

Self-promotion here, but my app, Supercoco, is far better for serious learners (Spanish only, iOS only). Focuses on speaking and listening rather than reading and writing, and is based on a large quantity of high quality content (about 300 conversations) that most apps just don’t have. https://supercocoapp.com

I wrote an article [0] recently about a method I used for learning Japanese using spaced repetition software.

Full disclosure, I wrote the software (Mochi).

[0] https://mochi.cards/blog/using-spaced-repetition-to-learn-a-...

No. The criticism of Duolingo is "it's an app", and not a native speaker or proper class.

Babbel offers much higher quality language courses (but has no free tier)

There is Busuu! https://www.busuu.com/

IMO, if you really want to get to a high intermediate or advanced level of proficiency, an app is never going to cut it. Nor are classes. It's worth the up-front effort - and less effort in the long run - to work out your own system.

There are a lot of individual apps and sites that can you can cobble together, and that play a part in a lot of people's personal systems. Spaced repetition is a great idea. But you will want to do it using a DIY-oriented app like Anki, and make your own flashcards. Forvo is a fantastic website and app for working on your pronunciation. For any popular language, YouTube will offer a wealth of channels offering video content (with transcripts) that you can use to get in your listening practice. Reverso is great for pinning down idioms. Just grab whatever grammar book from your local used bookstore (at least for starters - once you've spent a while learning, you'll have a better sense of what you want in a grammar book, and that's the time to pick a specific one and pay full retail price for it.) Once you're able to read a comic book or watch a slow-paced nature documentary in your target language (this is quite attainable within 6 months if you work steadily), get 1:1 tutoring on iTalki. Etc. etc.

The common criticisms about canned courses, at least according to a lot of folks in the recreational language learning community, are:

1. There's a speed limit. In a class, your pace is limited to that of your least motivated classmate. In a freemium app, you're limited by their monetization policy. With Rosetta Stone, you're limited by excessive animation crap in the UI.

2. You're stuck using whatever content someone else thought would be interesting. If it's not so interesting to you, your motivation is going to suffer.

3. You're stuck learning stuff in the order someone else thinks you should learn it. This can just murder your pace if, for example, the order in which your brain wants to pick up grammar rules doesn't exactly match what the course designer thought the right order should be. Which it won't.

4. Apps and courses sink way too much effort into metrics, either in order to assign grades or in order to gamify things or just to control your pacing. This creates a streetlight effect: They teach you what's easiest to drill on with short answer and multiple choice questions, not what's going to best enable you to use the language independently.

As for how a homegrown system should work, there are a lot of books and blog posts on that; I'm disinclined to endorse any one of them because it's better to read several and cobble together your favorite ideas into a system that's all your own than it is to follow just what happened to work for some other person. It's got to be your system that you worked out for yourself because it's got to be something you actually enjoy doing if you're going to have any chance of sticking with it for the long run.