Language Transfer is much, much better than Duolingo for learning a language.
I am learning Spanish using language transfer after having learned four other languages in more traditional ways. Obviously, immersion is the best way to learn. But if you have to learn any other way, this is the one. Far, far better than Duolingo.
It's made up of MP3s, usually about 10 minutes each. You just listen to them and respond to the instructor.
You can use SoundCloud, or YouTube, or the simple but practical smartphone app. The whole thing is run by one guy, and there is no charge but he asks for donations. I have been paying $10 per month on Patreon for several years now, and consider it well worth it.
You can learn French, Spanish, Italian, German, Greek, Turkish, and Swahili.
The problem with Language Transfer is its very limited language selection and its format.
Duolingo allows reading, writing, listening and speech (last two can be disabled if unsuitable in your context), and it does not impose daily limits. I've yet to find an alternative app that does all 5 of those things.
Yes, Language Transfer doesn't have as many languages as Duolingo. Hardly surprising, since the entire system and all the language lessons were created by one man!
For me, the most important thing is to learn to think in the other language. Everything else follows from that.
Language Transfer makes a conscious effort not to get you to memorize things, but to internalize them and understand the system. That works perfectly with my own way of learning.
I'd recommend starting with ANKI and looking up guides for that language. You might find add-ons that make it easier to use. While making your own deck is better, you can also download recommended decks to learn vocab. Otherwise there are open access textbooks and courses if you want more structured learning.
Is there anything with Japanese? It's the language I've been learning (I took a class and have been wanting to study it further), but not all language learning apps have it.
Paying a tutor or a class might be a good accelerant since you could ask fundamental questions in your native language. Once you have the grammar scaffolding, you could then use flashcards to start building vocab or looking for natives to share conversations with. Note also: immersion rarely works without some foundations to build on (unless the language in question is basically the same as your native language like Dutch is to English). The TL;DR is apps are more entertainment then education.
Depends. I've found that it was able to explain to me (about Spanish) why, when and how to use this form or the other. But it won't come up with a plan of lessons. And the level of support will depend on the amount of resources available for the language you want to learn