They Do It Different In Europe
Although 3/14 is recognized as the International Day of Mathematics, Pi Day is only a national holiday in the United States, where the dates are written in the MM-DD-YYYY format. On the other hand, Europe uses the DD-MM-YYYY format, making the connection between 3.14 and the date impossible until Europeans got creative.
Luckily for our math and pastry-loving friends across the pond, π can also be expressed as the fraction 22/7, which reduces down to 3.14. Coupling the fraction with the European date format gives them their own Pi Day date on July 22nd, which they call Pi Approximation Day or Casual Pi Day.