North America and Japan confirmed, Europe is waiting on a confirmation.
Looks like the two, very separate worlds will collide in two weeks. So far the event has been confirmed for North America and Japan; while Europe is still waiting for one.
Tweet from NintendoVS on Twitter:
A fresh wave of fun is inkoming to #Tetris99 with a special MAXIMUS CUP celebrating the final #Splatoon2 Splatfest! Compete in the Tetris 99 5th MAXIMUS CUP Splatfest Edition on 7/12, 12am PT – 7/15, 11:59pm PT & earn 100 event points to unlock a Splatoon 2 in-game theme!