I think written English and spoken English are actually two separate languages, at least in terms of how the brain treats it. Most people, when reading, will say the words inside their head. Translating, because they're fluent in spoken, not written.
I never really thought about this until I realised that I know someone who does the opposite. They translate spoken to written in their head, because they're fluent in written.
I'm not a linguist or a neurologist, of course. Just observing.
@Terrana you're right, I misspoke and didn't explain what I meant properly - spoken language is created by humans, yes, but written language is a technology.
Given slightly different circumstances, the writing system of any language could be completely different - maybe we'd be using a logography (like chinese) for english, or some other alphabet (based directly on futhark, perhaps?)
@lizardsquid Spoken language is also a human invention. Both of these things have evolved over time.