I speak english, spanish, japanese, and msa arabic. English is obviously my first language. I grew up in the bronx surrounded by latinos, I've ever had a good ear so i picked up alot of spanish from my surroundings. During Junior High My spanish teacher was sexy and I was trynna suck up to her so I was her best student. Her lessons plus my upbringing pretty much ensured me to be a fluent speaker by the time I graduated 8th grade(took her classes for two years). I Taught myself Japanese during college using a method very similar to Khatzumoto's(look him up!) AJATT method even before I knew who he was. Japanese took me about 16 months to reach business level fluency because I was immersed in japanese media for that whole time period. Arabic came to me naturally growing up muslim and reading Quran and such. Some dialects are hard for me to understand tho but they understand me just fine because I speak a formal dialect while they speak regional ones while also being educated in formal arabic.
My advice for learning a language is to immerse yourself in media of the target language for a minimum of 16 hours a day(Sleep hours count. Play media in the target language while you sleep. This helps your brain familiarize with the sounds and accents of the language. Study sentences and not vocabulary. Meaning learn a word in its context and not as a stand alone. The definitions for the english words "Place" and "Site" are virtually the same but you wouldn't say "I Work at a construction place" instead of a construction site. Mistakes like that are very common when we only learn language vocabulary and not context.