Even if you speak Polish, it's difficult to find an electrician, you often have to wait for a few months, especially if you want to have more done than some simple things like socket relocation.
Yes, you're right. I spoke to a Polish man last night and he also had problems getting an electrician and with them cancelling and so forth.
In this video, which appears to refer to AC current in the USA, the speaker says that it DOES matter which way an outlet is wired (ie where N and L are). He suggests it could otherwise be hazardous. There are many similar videos saying the same.
I would just add that I have UK extension sockets with a pilot light plugged in to the Polish circuit and those UK extension socket pilot lights glow even when the extension is plugged in but the switch on the wall is
off. What happens is that if I then turn "on" a connected extension socket switch the glow extinguishes and of course the connected appliance does not work. But this does show that current is flowing. This suggests to me that the RCD trip would not work unless the wiring was changed, I assume it would be a simple case of swapping the L and N over on the plug but I don't know because of course I'm not an electrician. Anyone using UK equipment in Poland and vice versa should speak to a qualified electrician before connecting things, so as to ensure usage is safe.
In a nut shell: don't assume your UK appliance in Poland is safely disconnected just because you switch off the socket, and vice versa. And don't assume the RCD would work if needed with appliances wired for the UK and vice versa if in the UK.