Books

I'm not the original commenter, but I am from Germany and was not raised other than learning English from fifth grade onwards. This was just the basics though, the bulk of my English proficiency comes from playing games, watching shows and movies and reading in English. In the beginning I did it to improve my English, but the German synchronization in videogames was especially bad, so I only ever play games in English, and adopted this practice for other types of media as well. On the rare occasion I find German books I like, I read it in German though, for example the fantasy books "Die Zwerge" by Bernhard Hennen.

Step 1: learn English for 7 years from grade 5 to 12

Step 2: the Internet exists and is overrun with Americans.

Step 3: profit

Once you are at the level where you don't translate words, but instead the words are linked in your mind to the concept itself, consuming media is no longer a chore.

It will probably be harder to learn a language other than English, because so much content is available in English (I know three YouTubers from the top of my head that create english content despite not being native speakers and one fiction writer). Though I obviously can't properly judge this as I only speak German and English. I have no idea if there is a Spanish focused YouTube for example. Due to the great firewall Chinese will probably be easiest to learn in that regard.