As I mentioned before, I have no experience with CC shops, so I defer to the experts on specific shop questions/problems.
I am thinking, though, that you would need to approach the shop the same way as any other group of html (or php) pages on your site. I.e. make a clone of the original shop and then modify the clone to 'make it Polish'. This would involve changing all file names to make them unique to the Polish shop (and site branch) and change all internal links to make sure that, once you are in the Polish branch of the site, you stay there until - and if - you deliberately click on a flag to go to the English version.
In the Polish shop you would then need to translate and change the text to Polish wherever needed and wherever possible. If there are words and phrases that are hard-coded in English, and that you may find impossible to change, you may have to put in brief explanations in Polish here and there...