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: 
In school, some of us learn Latin. We learn it because it is the root of many modern languages, so learning Latin helps us with understanding the modern languages.

Classical Latin is 2000 years old. Also, the fact that they call their language New English suggests that there's strong connections between New English and "modern" English (at least similar as "modern" English to Old English, though that's not very similar).
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.