There's a lot that goes into verbal intelligence, and we don't really know all of the what and how. It'd be cool if we did, but for now we can only really draw some correlations to physical areas of the brain, which are nevertheless fluid and unique in each individual, and some genetic links. Even then it isn't enough to account for half the stuff we observe humans doing – in Europe learning between 2-4 languages as a child is considered pretty much entirely normal.