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: 
800 years is a LOT of language evolution, but if they kept the alphabet, numbers and phonetics remained the same it would be a LOT easier than an unknown language in an unknown script.

A newspaper is written for a 10 year olds reading age, childrens English primers might be there as well. Textbooks, a whole bunch of stuff that would help.

The roots of words should still be discernible, Boewulf was written much longer than 800 years ago in a different script in Old English, but the Middle English version can be made out better with a bit of guesswork mainly because it's in our script

Your best bet is English primers and suchlike to get a feel for the language and basic vocab. Having said that English is one of the most complicated languages, so hopefully they have retained the grammar structure which is plausible since we have basically retained that since before English became English with no real changes.
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.