I would like to learn a couple of languages (polish and Japanese - I already learned Spanish to a decent degree) but it seems like every solution is closed source.
I would use books but listening (and speaking) are very important and books won’t help with those.
What would you guys recommend?
Duolingo is useful for wasting time while feeling like you are learning however it isn’t a great tool for learning if that is your goal.
I hear this opinion a lot, and I’d just like to add it manages to help with some exposure and repetition at the very least. I’m sure you’re more knowledgeable than myself with learning languages, but I’ve been using Duolingo to learn Japanese for a little while now and have managed to pick out basic hiragana and katakana here and piece together small words.
I don’t have any delusions that I’ll be fluent if I finish this course, but if it can help me learn the characters it’s worth the time to me.
A lot of people reduce Duolingo to their app, but they offer a big website on which you get a lot of explanations
I disagree, of course you can’t learn just using Duolingo, but it is like saying X textbook doesn’t teach you anything because you are only using that. Learning a language is a process that never ends and that requires a lot of different processes, maybe Duolingo doesn’t have absolutely all of them but if you finish a tree of the main languages and some other digging around you will have learnt quite a lot.