I headcanon that Wales would probably invite New Zealand even though she never gets invites.
England and Scotland would probably be the one who usually invites Wales and is already used to him inviting that... Sheep. Though, they're still annoyed by it, can't even have a trio talk without that sheep being there!
The thistle is the emblem of Scotland as a barefoot viking raider cried out in pain as he stood on one, alerting the Scottish army encampment that the Norse army were sneaking up on.