Isn't that what "en" on its own should be, though?

We should also enforce a standard where every website has to change their content to match the user’s preferred idiomatic diss, whether it be “yo momma”, “deez nuts”, “six seven”, or a series of hottentot tongue clicks recorded in Ogg Vorbiz.

en-DK is used for this in some cases, giving you English, but with metric units and an ISO keyboard among other things.

A dedicated one for International English, or heck, even just EU-English, would be great.

The EU websites just use en from what I can tell, but they also just use de, fr, sv, rather than specifying country (except pt-PT, which makes sense, since pt-BR is very common, but not relevant for the EU).

If you want to divide English into only two categories, I reckon US English (color, analyze, center) and International English (colour, analyse, centre) is the best divide. It’s imperfect—Canadians are mostly International but want analyze, and there are other controversial words like program/programme (US, CA and AU prefer program; GB and IN prefer programme)—but I think it’s the best divide if you want only two.

Windows distributes ISOs labelled English (en-US) and English International (en-GB) along this divide.

It’s also a valuable divide for reasons beyond language, because the USA really does have a habit of doing its own thing, even when pretty much the rest of the world has agreed on something different. Your US English locale can default to Fahrenheit, miles, pounds, Letter, and their bizarre middle-endian date format, while International English can default to Celsius, kilometres, kilograms, A4, and DD/MM/YYYY. It doesn’t sort out everything, but it gives a much better starting point. Not every non-American prefers DD/MM/YYYY, but even if they’d prefer something like DD.MM.YY or YYYY-MM-DD, DD/MM/YYYY is a whole lot better than MM/DD/YYYY.