Seriously, if Europe can do it with different languages, different cultures and even countries that used to be at war with each other
It's not working in Europe. Europe is not working. Europe is awash with illegal aliens who enter the Schengen zone through countries such as Greece that have poor border security, and are then free to move round.
It is more likely to work between AU and NZ due to their relative geographical isolation and a shared culture and language. It's easier to control when there are only two countries involved and no land borders.
In Europe, it's a disaster.