Chaucer isn't necessarily that bad. If you take the time, you can read much of it. For example, I think you or most HN readers could read and understand almost this entire passage if you know the framing story:

'And whan this goode man saugh that it was so, / As he that wys was and obedient / To kepe his foreward by his free assent, / He seyde, "Syn I shal bigynne the game, / What, welcome be the cut, a goddes name! / Now lat us ryde, and herkneth what I seye." / And with that word we ryden forth oure weye, / And he bigan with right a myrie cheere / His tale anon, and seyde as ye may heere...'

http://www.librarius.com/canttran/genpro/genpro824-860.htm

Almost definitely not. 4 quick dialects are AAVE, Indian English, Australian English, and, for a bit of localization, Iowan English. Mutually intelligible to someone who cares to pick up the slang, turns of phrase, and alternate grammars but clearly they are swiftly diverging.

I actually think NZ English is diverging the fastest. Some thing about being a small remote island nation that also has an indigenous language in regular use. Those guys come up with crazy new words all the time. What on earth is a Jandal?

Try Singlish (http://en.wikipedia.org/wiki/Singlish_vocabulary). Combined with their accent, it's a wonder if you understand anything at all when said with a lot of Singlish.

I live in Iowa. Is our dialect concrete enough to put it in a group with Indian English and Australian English?

I'm sorry, I can quite understand what you're asking.

Could you repost it in Australian English?

Probably not, but it is distinct enough from the south, the northeast, the PNW, and the west coast. I felt the need to localize a bit more than "American accent."

What makes you think it's not?

I think English will be different, but intelligible with Google Translate's 2599 edition. 2015 English -> 2599 English should be a cakewalk.

It will be intelligible, but will it still be art? English lends itself well to all manner of subtext. When what we call english today becomes a dead language, will it still even have the same meaning? It's something I occasionally wonder about Shakespeare. It's full of subtext and innuendo, but are we comprehending that subtext and innuendo the way they did back then? Probably not. The definitions of the words and phrases used are too different, let alone the subtext, idioms, etc.

I think you've answered your own question; we still appreciate Shakespeare as art, even if we can't get as much from it as a contemporary listener would. But historians, etc. can help fill in the gaps (much like reading Greek plays, etc.).