Aside from being about the US, he's talking about written English. Standard Written English is fairly similar even across regional accents in the US, and I'd say written English is more similar across the majority of the English speaking world than spoken English. (there are the gratuitous spelling changes introduced in the UK in the 1800s/early 1900s to differentiate from US convention, and some different words and conventions for group noun plurality, but aside from that very similar, whereas I have a harder time understanding some Scottish or East London speech than I do French or German.)
(there's also the accent/dialect/creyole/pidgin distinction, which often revolves around who has an army)
