Back in 1999 or thereabouts, the BBC (in collaboration with Russian television) produced an animated two-part series dramatizing Geoffrey Chaucer's classic stories:
Two versions of the series were produced: one in modern-day English, the other performed in the original Middle English.
Why would they have done that if the two versions were so similar? I've seen the Middle English version. It didn't sound much like "modern American English" to me.