Thanks for the tips.
Unfortunately, there are no solutions for me.
In my case, guest Login in ISE with special characters makes that ISE will send after correct authentication to WLC Information Access-Accept (Attribute Value Pairs - T = User-Name Val = łświder). The controller does not support special characters (łś etc.) and turns them into other characters. The controller creates a client session on WLC with a bad / changed login (in our case instead of "łświder" creates: "A, A.> wider"). I also do reports in Cisco Prime, where it also does not support special characters (Prime creates a new login "..> .. wider"). I know I can write in the instructions to not use special characters, but it will be difficult to maintain for my number of sponsors (there will be cases when the names and surnames are entered with special characters). So the best solution will be blocking the creation of such logins in ISE. In Cisco Prime, where we have previously created a guest account, there was no possibility to create accounts with special characters, I think that the best solution would be to prohibit special characters in logins in ISE.