As an Irish resident, you are assessable to CGT on foreign gains. When you sell the property, you will need to calculate your Irish CGT position according to Irish CGT rules in force at that time. Any Bulgarian CGT you also pay can be used as a credit against your Irish liability, presuming of course that the double tax treaty between the countries is still in place at that stage.
Despite what the last poster said, the fact that you pay Bulgarian CGT does not automatically exempt you from Irish CGT.