Great question! Constant Contact supports the ISO 8859-1 standard for character encoding. We do have a specific list of languages, and unfortunately the Polish alphabet isn't supported at this time. We recommend a using a Polish Keyboard layout or searching online for additional resources.
It is possible to get Polish letters into your email, but only using HTML coding. You will need to access the block’s HTML code where you want the character and insert the code within the text and hit “Update” for the block. Here is an external resource for polish characters HMTL codes.
I am very sorry for the confusion, however, the Polish alphabet is not supported by our system - no matter the different coding that you can try. If you're using a PC you can search online for the instructions to try adding and utilizing a Polish keyboard layout when typing the text for your email. The only other option would be to insert the Polish z as an image within the text. I hope this helps!