By Law, all the countries within the EU exchange depositor’s details with each other, under the European Savings Directive, if they are earning deposit interest without deduction of DIRT tax.
However, if you are already paying DIRT tax in Germany, then the Irish Revenue will give you credit for this & if the rate of deduction is in excess of 25%, then you will be entitled to a refund for the difference.
You should obtain a Certificate of Interest from the German Bank for each of the tax years & return them to the Irish Revenue together with your normal end of year return(s).