Is the ability to acquire language innate or learned?

I think the ability to acquire language is something that people is born with.
During vacation I met my friends who also study abroad. They are all native Korean, so English is their second language. While some of my friends speak really good English, some do not. We all began at the same level, but the levels we ended up with were all different. Some are as good as native speaker, some are still bad. Those who speak good English, among my friends, were origianlly really skilled at language. They were extremly skillful at Korean than the others. For them, who are skillful at language (at any language), acquiring language would be much eaiser than other people and it would take less time than the others. Therefore the ability to acquire language, in my opinion, is innate.