3 years for fluency; Learned by myself. It was Japanese, not that difficult. You can try to look for materials on reddit, since there are many subreddits dedicated to learning specific languages. I usually look for word lists online and get my grammar polished on youtube. Flashcards are also nice for vocab.
When you've got the basics down, aka. the sentence structure, he/she/it/you/me/they/them, basic verb conjugations and a sizable enough vocabulary, feel free to just listen to podcasts or watch streamers in that language.
Good luck if you're planning to learn.
I wanted to learn Italian and it took me almost 2 years at first I had an American accent now I got better but most of the people say that they know Italian very well but the only thing they know is "pasta, spaghetti,mamma mia and lasagna"
I learned English in about 2,5 years. My mother language and English use the exact same alphabet just different pronunciation, so it's not that hard. The hardest thing for me at the beginning were the pronunciation and gender thing (like she/he, hen/rooster, etc.)
For people who have learned a new language, how long did it take you? Did you learn by yourself or take lessons somewhere?