!. If you want to hire a tranlsator it'll be quite expensive - they may charge $100 a day.
2. There are a lot of people in Poland who speak English and I'm sure you will find somebody who can help you.
3. If you don't know anybody English-speaking there, try to find an English school - lots of students to practise the language.
BTW, are you travelling only to Koszalin?