>>74629
It depends how realistic you want to make it. For hard-realism, anything more than a few hundred years and you're already looking at merely the languages being incomparable to anything spoken today. For example, here's what English was like 1000 years ago (from the opening lines of Beowulf):
Hwæt! Wé Gárdena in géardagum
þéodcyninga þrym gefrúnon·
Also keep in mind that while Beowulf was transcribed into the Latin alphabet (where possible) for a manuscript post-dating the original poem likely by centuries, Old English from earlier was written using runes. So it not only doesn't SOUND like modern English, it doesn't LOOK like it, either.
Of course, all religion and culture is going to be completely different, too. Probably even more than historical precedent suggests, because modern technological changes and globalization are accelerating cultural drift.