Do I write them? Call them?
I can't make your decisions for you, but if it were me and the places you've found have phone numbers I would call them.
If they don't speak good English, then don't go any further with the particular rental.
Before I would even think about getting on a plane, I would want to know the answers to basic questions regarding rental.
1. What is included in the rent and how much is payable in advance? Water, heating, gas and electric? If you have a specific budget you are sticking to, you need to know of any added costs.
2. Czynsz is a monthly payment toward building maintenance and includes such things as rubbish removal, cleaning of communal areas, gas inspections etc. I think this payment can apply to tenants as well as owners, but I'm not 100% on this. Ask if this is included or extra.
3. Can your contract be renewed at the end of the term? If you like where you will be living, you won't want to have to find a new place maybe 6 months later.
4. How much is the deposit, and if for any reason you decide to move out before the end of the term, is it refundable in full or in part?
These are questions I've thought of off the top of my head, you will probably think of more.
If you get the answers to your questions, then it's up to you whether you decide to go and view a property.
Most apartments in Poland are furnished, so if you do go and see one, check that there is an inventory of everything in the apartment, and that nothing is broken, or further down the line you might find yourself being billed for any breakages, appliances not working etc.
Also check windows etc, old buildings may not have windows in the best of conditions, and you won't want to freeze to death in winter.
Lastly, Peterweg is right. I would not consider signing a contract in another language I don't understand, you will need to get it translated. Personally I wouldn't rely on Google Translate to give an accurate translation of something so important.