I have also noticed that when you read the word ”metaethics” on Lesswrong it can mean anything that is in some way related to morality.
Mayby I should take it upon myself to write a short essay on metaethics and how it differs from normative ethics and why it may be of importance to AI alignment.
I think we can overcome most of the cultural differences you mention. In my lifetime we have become noticably more culturally united and I believe the kids who grow up today will be culturally more or less the same across Europe.
A much bigger impediment to European unification is instead something you don’t talk about namely the different political cultures in Europe, including such things as the level of tolerated political corruption.
These differences are also shrinking but there is still some ways to go, I think.