I'm tri-lingual, and can make myself understood for basic stuff and can generally get the gist in 3 more. I learned English by immersion in my teens, probably the ideal age. When I arrived in America, beginning of summer, I joined all youth summer activities available in town; baseball, archery, joined a Scout group, etc. I made friends and was interacting in English constantly. By School start, I was placed in regular classes. My sister didn't do these things and was placed in many English for learners classes, with foreign students. I speak much better than her.

Also, I watched Sesame Street, Mr Roger's, and other children's shows

My kids have not lived in an English speaking country, but game in English, watch all media in English, with subtitles in English, and attended bi-lingual schools. I spoke in English with them a lot while they were growing up. They speak very good English, with my daughter having EU C2 level, the highest official level in a foreign language.

Watching foreign media, with subtitles in that language, including children's shows, reading foreign news and stuff, etc. helps a lot.

Also, in many areas there are foreign language oriented Meetups.