1) At school obviously
Though to get reasonably good at it (I think I can say I am without overreaching) I had to consume metric tons of English language media of all sorts. TV shows/movies probably help the most. My spoken English is horribly accented though, because all my English usage is from passive media. I don't get to actually say out loud more than a dozen sentences in English every year. Oh for full disclosure, I also studied English at university level for a semester. Ultimately I decided against pursuing it though, job chances with it are shitty as hell and in that one semester, honestly I didn't learn anything new.
2) The strength of English is the simplicity, even if you do something wrong, people will figure out what you meant 99% of the time. The weakness is also the simplicity. English is inaccurate and limited. German has many more words, so for many things we have finer connotational differences (don't ask me for examples though). But in everday use I doubt it makes a difference, as proven by my difficulty to actually come up with an example.
3) Well why do you think when I was translating a video game I was translating it to English and not to German? I can either reach an international audience from all age and education groups or I can target German children before the age of 16 or people who are so dumb that they had to drop out of school entirely. I know that sounds harsh. but video game English is really not hard... English is the lingua franca
currently used in the world to reach everyone, so basically all websites which might be interesting to more than a local audience are in English. It's as simple as that.