I learned but I learned quite early, being an exchange student twice (high school and university, one year each). So I've been pretty much fluent since I was 1

I learned but I learned quite early, being an exchange student twice (high school and university, one year each). So I've been pretty much fluent since I was 17, which I realize is much easier than moving there in your 20's/30's. But if you're in Germany I recommend immersion -- try hard to make friends who don't speak English or at least won't automatically switch into English all the time. That and the Volkshochschule. Out of country yeah, I think Goethe Institute is the way to go if it's available where you are. Just based on reputation, but it's also a path into the German university system if you're interested in that.