Witam, kilka pytań, jestem nowy tutaj.

Hello and welcome aboard, @Olszax. What you should do in this case is join the server and see it for yourself if you'll like it or not, there is a reason why so many people are playing here so they obviously love the community and everything about it. We are by far one of the most popular realms and most likely the oldest still standing and rocking hard after more than 13 years online.
As for using a polish diablo client, you'll need to find the diablo2 polish installer but I highly recommend you stick to the english client. Also don't forget to read the connect instructions as you're required to install a custom patch to play here which you can download from our website and make sure to read the server rules as well.