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.