My understanding is that each country could have more than one official language like with Ireland they can have English together with Irish? And there's also Malta 在 2018年9月17日週一 18:14，Tony Finch <dot@dotat.at> 寫道：
Clive D.W. Feather <clive@davros.org> wrote:
It will remain an official EU language because of Ireland (Irish has
never
been an official EU language).
Irish has been an official working language since 2007 - http://ec.europa.eu/education/official-languages-eu-0_en
But it's more complicated than that: Irish has been a "treaty language" since 1973, which means it was official in some (but not all) contexts. And since 2007 there is a derogation which says not all documents have to be translated into Irish; this derogation will end by 2022.
There's a fairly good summary at https://en.wikipedia.org/wiki/Languages_of_the_European_Union#Irish with some discussion of the arguments around the status of English a few paragraphs below.
Tony. -- f.anthony.n.finch <dot@dotat.at> http://dotat.at/ Shannon: South becoming cyclonic 6 to gale 8, decreasing 4 or 5 later. Moderate or rough becoming rough or very rough. Rain or showers. Good, occasionally poor.