rosegold: I'm not sure if Steve does or does not know another language. I do know that in his article
Self-Help Junkies he lists "learning a foreign language" as a way to measure your personal growth. He's also mentioned many times that it's a good way to improve yourself, and stretch your mind.
Learning a language forces you to think in a new way, it also gives you another tool in which to solve problems. Many problems are also the cause of specific language deficiencies, which learning another language would solve. On top of that, learning another language you can communicate with people who speak that language. You can learn about the culture and the history in the language it was written and you can enjoy things like foreign film and music more.
Personal Development isn't just something you focus on, because by itself it's meaningless. It's something you apply to the content of your life. You enrich all parts of it by following your own personal path of growth. You don't have to either, it's an opportunity, and only us humans have it.
As for "you lose it when you die", then why grow at all? You can't keep anything that happens when you are alive, except, perhaps, maybe, possibly, your experiences.
Zwynd: Awesome! You sound inspired, go out and do it. If you get discouraged by it later, great!
I'm not sure if you have to stick to one thing, although out modern society keeps telling us we have to. I want to do 50 different things, or more, but I need to facilitate a way to do it as well, that's really the big question. Leonardo DaVinci had close to 100 hobbies from painting, sketching and sculptin to maths, physics and the sciences. He's unquestionably a genius and he didn't stick to just one subject.
As for advice, the only advice I can give is to follow your dreams, because they are yours and noone else can fulfill them. Also, make a list of everything you'd like to accomplish, then use that to get a map of where you'd like to go next.