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).