My recommendation is actually the opposite of what you are asking for. Language Transfer is a series of audio files where you hear a teacher speaking to a student in a kind of Socratic dialogue.

Everything is completely free. You can find it on YouTube, SoundCloud, download MP3s, or use the simple but very effective app. I have been supporting it with monthly donations for about 5 years.

There are courses for French, German, Spanish, Italian, Greek, Turkish, Arabic, Swahili, and for Spanish speakers wanting to learn English. British Sign Language and Japanese are coming. Some of these are introductory courses, others are more complete.

In addition to my native English,I have learned one language in school, and three more by immersion + lessons) self-study. I have to say that Language Transfer is the best system I have ever used.

The emphasis is on internalizing, and developing strategies for retrieving information in your brain, rather than wrote memorization. I found that I retained knowledge much better, and it has lasted longer.

I’ve been using Duolingo to learn a language for a few years now, enjoy it, and feel that I continue to progress. I know there are other apps out there as well but I don’t have any experience with them. Duo does have a gamification component to it — some of which you can disable, but not all — and there is a cost if you choose to subscribe.

For me, though, I’m likely going to need to immerse myself and/or take a few formal classes to get better at conversational speaking as I keep learning. Not many folks around me learning German. The app does help practice conversations and give tips, which is nice, but using a language in real life with another person is more effective for me.

Anki for flashcards and a lovely local teacher that I go to once a week (not a university classroom). The real truth is it takes between 1000-4000 hours depending on your language, and the only way to get that is by doing a little bit every day. I'm probably somewhere around 700 hours after three years.

Immersion.

Comprehensible input is far and away the best way to learn a language. If the language you want to learn is Spanish, I highly recommend Dreaming Spanish. I believe there is also a French version.

If you want a different language than above, search "Comprehensible Input [target language]" and you should be able to find lists of resources in your target language.

The real answer is rough, because there are no shortcuts.

The best way to do it is the same way you learned your primary language. Learn just enough through study to be able to use a little bit of the language, and then actually start using it.

Talk with people who speak it, and learn to read and write all over again. Sound like a tourist for a couple years as you pick up more and more. Eventually you'll be fluent.

The best method is the one you can stick to.

What works great for me, is boring to another one. Even if I have the most optimal way of learning, if you abandon that, you won't learn anything.

That said, the availability of podcasts, videos, online courses, AI for checking your output, asking follow-up questions, and having real time conversations, are all tools we could have only dreamed of even 10 years ago. Even if people here dismiss the use of AI, it will get you up to CEFR B2/C1 level easily.

I've heard watching kid's shows in the language you'd like to learn works pretty well for newbies.

leaving trial by fire