What is the alternative to Duolingo that has worked best for you? I’m especially interested in learning Japanese

Try ankiweb.net or the ankidroid android app to download flashcards for all sorts of things. Basically users make custom decks and you can download them for your own use or even make your own.

If you're serious about becoming fluent, apps will not give that to you. Ditch everything else and focus on input.

More here: https://refold.la/simplified/

I agree. This website has been very useful and encouraging on my language learning journey.
- Another vote for Refold here!
I feel like it depends a bit on the language you're learning, which one you're coming from, how your brain works, and how much you're willing to think about the exercises instead of just doing them.

I'm currently using Duolingo to learn esperanto, which is admittedly a bit of an oddball language since it's a constructed language and the grammar follows pretty simple rules. Ive been at it for a bit over a year and while I still have a long way to go, I feel like I'm well on my way to being fluent, mostly I need to pad out my vocabulary more, and my ear could use more training.

It helps that a lot of the words look/sound pretty familiar to me as an English speaker, and the kind of person who likes picking the sentences apart a bit and actually figuring out the grammar and such as I'm going.

I took a few years of french in high school, none of it really stuck, and I think the traditional classroom approach just doesn't work very well for me in learning a language. But I think if I had something like Duolingo at the time where I was just kind of thrown to the wolves and made to figure it out myself I would have been more successful
- I use Duolingo for Spanish but also practice with Spanish speakers. I also click on the forum stuff for info on grammar, because I don't think the grammar really comes through in the app if you don't already know the gist of the rules. Or I look it up in a Spanish text.
  
  But the vocab practice i do find helpful.

I'm trying to use a combination of Genki and Renshuu, but learning this on your own is still incredibly rough.

I would recommend staying away from Duolingo, personally, because it not only heavily promotes memorization over understanding, but also often teaches you things completely wrong. This doesn't apply to just Japanese, and it's matching the experience of other people I've talked to

Nothing beats creating your own deck. Check out Anki as others have mentioned. Back before starting university when I still had time/motivation, I used the Yomichan browser extension to create flash cards out of sentences I come across online.

I can really recommend Wanikani, mainly focused on learning kanji.

For grammar: the Genki books and online explanations like tokini Andi.

Everything else is Anki.

Yes this is a lot. I'm currently doing wanikani only because of time issues, but that's what I found pretty effective for me. じゃね！

I stopped doing lessons on wanikani after level 20 because I found while I learned a lot of kanji and vocab, many enlightened and burned words started to fade. Plus there's many common words which you don't learn even after a year of studying, even though you really should imo. So I switched to sentence mining with Anki and it's been pretty good so far, although I don't understand much, I hope that comes with time

For Japanese Wani Kani and BunPro are both good for learning kanji and grammar respectively

I kind of gave up on Japanese years ago, but I've been trying to learn Korean for a couple months now. I started with Duolingo (great for basics like the alphabet, and in general for reminding you to practice everyday), then added YuSpeak (similar to Duolingo but way better paced/structured and with some useful systems to keep track of your weak points and review words and concepts effectively. Their Japanese course has even more features).

Although the apps are a great way to start, like other commenters said, they really promote memorizing over understanding/using the language, especially Duolingo. So the greatest addition for me so far was actually ChatGPT (GPT 4). Now I can learn a new concept on YuSpeak or Duo and then immediately go ask ChatGPT to go over it together and make up some exercises for me to do. It really works surprisingly well, and in just the few days since I've started using it, it feels like my ability to write and read the language has improved exponentially compared to when I was only using the apps. I also fare much better in the apps themselves.

Of course ChatGPT is not 100% accurate, as we all know, but it opens up so many learning avenues that it doesn't really matter, especially if you're a beginner to intermediate student. Obviously it also can't completely replace an actual teacher (on the other hand, it's available 24/7, unlike an actual teacher, and it's much cheaper too) and it won't help with listening or speaking, but using it in conjunction with apps and a YouTube video here and there really creates a pretty effective and proactive learning environment.

TL;DR: Check out YuSpeak and consider using ChatGPT 4.

Duolingo isn't especially good for Japanese. It works better for languages more similar to English in sentence structure where you're making more simple substitutions between English and foreign words.

I second WaniKani as being good for learning kanji, but for grammar I think an old-school textbook/workbook is really helpful in learning the basics. I like Genki I & II as a grammar tutorial but there are others like Minna no Nihongo that others like more.

Heh. Same thing for Rosetta Stone. I tried that before moving to Japan, and it was too much "english translated" to be overly useful. I ended up with private lessons using the minna no nihongo series, and it wasn't bad, once you get over the fact that the vocabulary (at least in the beginning) is more slated to incoming factory workers than office types. I can't see that being overly good for self study, unless you live in country though.

A teacher

I enjoyed LingoDeer for Japanese!

If reading and writing are low priority, Pimsleur audio is my go to way to learn a bit of a language quickly before going somewhere. The app gives a free 1hr of every language so it’s a great way to try without getting stuck in a free trial you forget to cancel. Strongly recommend, as someone who has tried duolingo, clozemaster, and lingodeer in the past, Pimsleur is my preferred method for me by far.

A friend swears by https://www.clozemaster.com/

Download some Japanese textbooks and go through them in order. They cover important vocab and grammar and conjugation, and have exercises and worksheets if you get all the right versions. I have the Genki textbooks and the situational functional Japanese textbooks myself, I recommend those. You can get them on Zlib I believe. For Kanji practice use Kanji Tree or Wanikani.

If you have a local college or university that offers Japanese classes, those are your best option if you can afford it. They also often provide the occasional opportunity to travel to Japan for relatively cheap.

If you are just getting started, this is a good resource for learning hiragana and katakana.

Past that, I used Anki and Bunpro for learning vocab and grammar. However, an alternative to anki for vocab that's definitely worth checking out is jpdb.io, and Cure Dolly's youtube videos are good for learning grammar.

There are also some decks that people have on anki which have sentences that you can practice on, I hear those are a pretty good way to start reading so that you can work your way to reading books/manga and stuff.

Here's another website that's worth reading through if you're interested in doing immersion learning with japanese.

I use an android app called kanji study to help learn/practice writing kanji. Once you have the basics down, writing characters helps a lot since it helps you recognize radicals that appear all the time (and helps a lot with remembering characters)

https://play.google.com/store/apps/details?id=com.mindtwisted.kanjistudy

On top of what everyone has said, Ringotan is pretty nice for learning Kanji