All in all it wouldn´t be a problem if I only intended to sail in Portugal (or charter in Croatia, for example), but I am living here right now and I would really like to charter a boat locally (inland waters). I cannot apply for an ICC (accepted locally) because they are not issued to any other EU countries beside UK…
The Irish Sailing Association is empowered by the Government of Ireland to issue ICC Certificates to persons passing the relevant assessment. You could sign up with an Irish sailing school for the 2-day course/assessment as your English seems to be good enough.
Flights from Prague to Dublin would probably be cheap for a weekend break, as the traffic is normally in the opposite direction