English is ubiquitous. Even if it's not your mothers tongue, it's just a click away from a vast source of resources and places to practice it. Once you get the basic gasps of the grammar, the rest is just practice and adding upon it. There's certainly a learning curve with the grammar that's about the hardest thing to get used to, but I think once you get a second language going, if you pick up on another one it gets easier with time as you kinda switch mindsets easily. The earlier in life you get to learn another language, the better.
And about vocabulary, you never stop learning new terms throughout your life. The big issue comes when you try to learn a language where no one in your community speaks it (or just a few). If you don't practice, it slowly fades away.
Speaking 2 or more languages is not a big deal in some places.