Substitution cipher. Code rotation is in the story.

(Basically, because it's been some time now for people to enjoy breaking it: take the first line of code:

JMPWF ZPVBO EJNJT TZPVB OEJTX

Now, count back one letter from each of those:

ILOVE YOUAN DIMIS SYOUA NDISW

and so on. Obviously, you'll need to form them back into words rather than five-letter blocks.

"Code rotation" means that you count back in different directions. Oh, and the Polish one? Is in Polish. Poltran-translated Polish, but Polish nonetheless.