What you're describing doesn't quite sound like a DNS leak.
Czechia and Germany are neighboring countries. It's quite possible that the nearest optimal DNS server is located in Germany. This isn't a 100% guarantee, but you can check the city location of your proxy IP at
https://ipinfo.io/. If it's a city in the part of Czechia closest to the German border, then you can probably relax.
Of course, if your proxy provider allows it, you can manually set the DNS server selection. But are you sure this will make things better?
I agree with Turelink that it might be somewhat pointless to look for problems unless you've encountered
real issues with the proxy's operation. Sometimes, you might start worrying about something that isn't actually a problem at all.