If you go back half a millennium, most languages are the same.

The sign above the door at the primary school outside Karlstejn Castle is unreadable to a speaker of modern Czech.

School website: https://www.skolakarlstejn.cz/

Better pics can be found easily.

It's quite rare for a language to remain close enough to be intelligible.

English is a mongrel, with influences from old French and ancient Saxon and Norse and Celtic. Every few centuries you go back, you strip away whole layers of additional vocabulary left by the descendants of successive invasions.