Question: Out in the former state of Utah, near where the Old Salt Lake ruins are, a group of scholars and students from the New Jerusalem University are on an exploration mission. They have heard, from an unknown but (maybe) reliable source that an old Fallout Shelter is out there. They search all day until they find it. They ask, or rather force, some slaves to break down the door, and they are able to get in. 

The Fallout Shelter, though littered with skeletons, is full of valuable knowledge from before WWIII. The paper they used in the Old Times was super powerful, and never rotted, at all. Most of the notes the found were just grocery lists and etc. but they do find a blueprint which talks about some machine powered by that mystical force, the “electron” if I remember correctly. 

There is just one problem. The apocalypse was 800 years ago, and since that time New English (The language they speak in the present) is totally different from Modern English. So, what might be a plausible reason for why the college kids could read Modern English?

Answer: 
Languages tend to develop fastest in cities, where lots of people meet and develop new words and new grammar. Outside the cities, especially in isolated communities, language change is slower. There are parts of Sardinia that have an Italian dialect that would probably be intelligible to the Romans. If this is the case it may be that a slave can read what the intellectuals cannot.

*Modern English is a foreign language to the intellectuals of New Jerusalem, but out in the wilds of Utah, among the backwoodsmen, you will still find families who speak a language that, while it isn't classical English, could be understood by a person from the times before the war.* 

*Among the slaves is LeVerl, and he grew up in an old isolated family (before his capture and enslavement), and while he has since learned to speak New, he still knows the language that his mother learned from her father. To the scholars’ surprise he can read the old texts.*
Basic electrical machinery - such as a dynamo, or an electric motor - could easily be described simply through images, schematic diagrams, and other visual means. The scholars would need to experiment with the proper materials\*, but the actual design would be easy to pick up on. Once they have a handle on what those basic machines do and how, that gives them a starting point to translate documentation related to those machines, which is a big leg up when working on other schematics.

\*They might not have to guess if the materials are described *chemically*; I would expect chemical symbols for elements to be pretty stable (no pun intended). They're already short, unambiguous, and half of them are already Latin or Greek, so it's not like they're neologisms that will wear out.