Q: HBO GO availability for Apple TV 4.gen at my country App Store (Czech)

the app is pointless if hbo go is not active in your country so if they don't bring support to czech then having an app would be pointless it would just ask for a login you did not have or fail because the ip range was for a unsupported country

Just to double check, which do you have in the Czech Republic—HBO Go (linked to a cable TV subscription of the channel) or HBO Now (monthly subscription).

HBO Go requires that you have a subscription to HBO through your cable tv provider. Is that what you have?

You may want to reach out to HBO to see if they can provide this detail. I see that HBO Go is offered for iOS there. Try contacting HBO Support: http://www.hbogo.cz/