@veggie_eric
Duolingo helps but should be only be used as one of the many tools
I speak more than 7 languages, few fluently, few intermediate and rest on a mid-high beginner levels
Depending on the languages, beside duolingo, you can:
1. Use Michel Thomas or language transfer (free)
2. Use anki flash card
3. Watch YouTuber videos (those that comes with subtitles with the language you're learning)
3.1. Watch it without subtitles, then re-watch with subtitles then go through transcript, rmb as much as you can then watch it without sub again
4. Use sporcle to find quizzes (I find it useful for verb conjugation quizzes)
5. 1 to 1 tutor on italki
6. Try to read and write daily in the language you're learning (even 15mins is good enough)
7. Speak as much as you can, even to yourself like, I'm eating a cake, I'm drinking water, I was busy - mastering the top 100 verbs, especially with grammar conjugation
8. Watch videos and put subtitle beside, then try to imitate and articulate the same way
9. Practice and practice, never be shy in speaking even if you speak like a baby with no sense of grammar - no native speakers care or judge, they will be more than proud that you're learning their languages.
These are what I can think of now
I've sped run using these methods learning some languages like French and Spanish as fast as a month or so to be able to speak with native speakers, as least like a baby - able to really say 50% what I would like to say
Since then I've repeated the same with a few other languages so I hope these help
