In Finnish we have “kissanristiäiset” (literally means a cat’s christening), which means some trivial and meaningless celebration/event.
I’ve been learning Scots gaidhlig which has some really great ones:
As happy as a mouse in a loaf (really happy)
As happy as a shoe (not happy at all)
As fat as a seal (very fat)
As full as an egg (couldn’t be fuller)
As wet as a cormorant (soaked)
As bald as a shinty ball (hairless)
There are many others.