I have a cheesy headcanon that each region has their own wedding traditions loosely connected to their game counterparts.
Like in Unova, it’s traditional for guests to only wear black and white to pay respect to Reshiram and Zekrom and wish the bride and groom a harmonious marriage.
Or in Sinnoh, the tradition of a diamond engagement ring is rooted in the belief that Dialga will grant them a long life together, and the bride wears pearls to commemorate the new ‘space’ they are forging as a newly joined couple.