Not 100% sure but I bet a German card won't work, and this is the reason of why they have different cards for different countries: I think the country of your card must match the country of your PSN account.
But now that you mention it, I remember to have seen in some stores that instead of having a country as their region (UK, FR, IT, ES...) they had EU instead. I'm not sure but I'd bet these cards would work for all European stores.
Ireland is one of the countries supported by PS Now:
**Current markets where PlayStation Now is available: US, Canada, Japan, UK, France, Germany, Belgium, Netherlands, Luxembourg, Austria, Switzerland, Ireland, Spain, Italy, Portugal, Norway, Denmark, Finland, and Sweden.
At the launch of the new PS+
they'll add more countries:
Bulgaria
Croatia
Czech Republic
Greece
Hungary
Malta
Poland
Republic of Cyprus
Romania
Slovakia
Slovenia
So the list will be increased until 30 countries. As reference, Game Pass Ultimate's xCloud is
available in 26 countries. Same as PS Now but removing Luxembourg, Bulgaria, Croatia, Greece, Malta, Cyprus, Romania, Slovenia and adding Australia, Brazil, Korea, Mexico.
So yes, starting next month PS Now (well, PS+ Premium cloud gaming) will be available in more countries than Game Pass Ultimate's Cloud gaming.