You may only download from the App Store for the country of your legal residence. To use a store for a particular country you must be a legal resident and provide a verifiable payment method for that country. If that is a bank card it must be from a bank in that country and have a verifiable billing address in that country.
If you qualify as explained and change your account to the German store, everything in the Purchased list from the Irish store will disappear, the list is store specific. Willy nilly changing your account from country to country can cause quite a mess.
As Niel suggests, ask the developer to offer the app in your nations store.
ASC - Late 2012 Mac mini, macOS 10.12.5; Watch, 38 mm silver AL, watchOS 3.2.2; iPad Air 2 & iPhone 7+, iOS 10.3.2; TV 4th Gen, tvOS 10.2.1; Airport Express