The main language spoken by the vast majority of people in Poland is Polish. In the centre of cities such as Warsaw and Krakow, English is widely spoken.
Most people under the age of 35 understand English reasonable well. However, older poles outside of the main cities will speak little or no English at all. In the outside areas, the people there will often understand German or Russia. Signs in English will often be found in the tourist areas of the city, but not once you go further outside the city.