It's a national language in Malta, making it a popular destination for "language weeks" in European schools, where English is usually a main subject.

That’s not why it is an official EU language, however.

English at this point has stopped culturally belonging to the United Kingdom and whilst one can discus it's not so very moral way of getting there, it's become the bridge language for people of different languages to communicate in, further solidified by the internet.

That said, whenever there is a language selection UI (e.g. at banking machines or institutional websites) in wider Europe that uses flags to represent languages -- probably not a good idea to start with, but very common -- the Irish tricolour should be used to indicate English rather than the UK or USA flags. (although cf Airteagal 8 of Bunreacht na hÉireann).

Relatively few people would recognize that it’s meant to stand for English (including myself), so I’m unconvinced that this would be better.

Cool, so the European Union and overlapping institutions could see this as an opportunity to promote greater public knowledge about one of their respective member states. Seems like an argument in favour of encouraging the display of a member state's flag rather than that of a non-member-state or former member state (especially given that state's history with respect to Ireland).

Using flags alone is already poor UI since there are many languages which spill across the borders into multiple member states and non-member states, and some member states with multiple official and commonly spoken languages.

But a menu item that reads: [Irish flag] (English) like one that reads [Swedish flag] (Svenska) does not seem worse than the legacy use of the UK flag or the popular use of the US one.

This is how we end up with a white box 'flag' that says 'en'