What is the difference between kosher dill pickles and Polish dill pickles?
Those are two different processes. Unfortunately English language don't have two words for the outcome and they are both called "pickles".

Usually Polish pickles "kiszony" should be made with: 
cucumbers, dill, fresh horseradish, garlic and salt. No vinegar.
Kosher pickles, called in polish "korniszony", are made with brine that contain vinegar. 

I assume that those two recipes have been mixed outside Poland and both things are "korniszony" with the difference that "polish ones" call for ingredients used in "kiszony". The difference in taste is that polish one is much more spicy while kosher one is sweet.