I started learning Russian two years ago via youtube channel “Be fluent in Russian”, and later added Polish when I downloaded Duolingo.
Duolingo is okay, but the seminars by independent youtubers offer a better understanding and pronunciation guide.
Also listening to music in the language is good. That was how I started learning Polish.
I can read and speak French pretty well. But understanding spoken French, forget it, unless you are sure of the context. Plus French speakers use a lot of slang.
I started learning Polish on YT as well.
I also want to learn Mandarin.