I am self-taught*, and I have some degree fluency.
*In my case, I had a friend who tutored me on pronunciation and pitch for a couple of months, which was a great help. Then, I had a girlfriend here in Japan, a side-effect of which was a rapid expansion of vocabulary. Then, I got a proper job in Japan, and another girlfriend (Mrs. Majestic) and those things really propelled my Japanese knowledge. Then, finally, I became a manager at work, and I had some direct reports who constantly helped me to expand my understanding of the language. Now I'm mostly self-study (purely by myself). I couldn't have become anything close to fluent had I been in complete isolation. That's an amazing journey to fluency! It's inspiring how many supportive people you had along the way. I've found that self-study, combined with insights from various sources, can make a huge difference. Sometimes sites like
https://personalstatementhelper.com/ post helpful articles on structure or writing tips—though I see them more as an extra tool than a main resource. In the end, your motivation and real-life practice will always be the biggest factors in your progress. Keep exploring and trying new methods, and your language skills will keep growing!
Self-taught in my case means no formal Japanese language classes, but there sure were a lot of people around me who supported me.