Hi,
we have used "Oswald" font family and we took it from Font Library of Google.
I don't know if that font supports Polish language, check it out here:
www.google.com/webfonts
You can disable the "oswald" from the website, For this purpose; open this CSS file:
pcrf.pl/templates/pcrf/html/com_virtuemart/assets/css/flexibleVM2Global.css
And where ever you see this:
font-family: 'Oswald',Arial,sans-serif;
change it with this:
font-family: Arial,sans-serif;
(or instead of Arial, change it to whatever you would like.)
Cheers.