zoogle, When stopped by the cops you need a drivers license, registration and proof of insurance. If you are going to get it registered in Poland you need the Title and Registration then you need to buy insurance.
Just remember when importing a car to Poland make sure you have had it in your possession for over 6 months or you will pay 42% duty based on the car purchase price.
And you can travel on a valid registration from the US or Canada.
The language will be easier when you live there. You will have to speak it. However, if you move to a large town there are more english speakers there. I was 11km from a town of 18 thousand and you had to know Polish. private teaching is desired by most Poles. The schools teach the British english and not the American english.