5.56mm
Perhaps you can volunteer to teach the class :-)!
I grew up pre VCII when the only Mass celebrated was the one now referred to as the TLM. My mother worked for an international airline. I still recall flying to Denmark at age 5 and attending Mass in Copenhagen. As you pointed out, because of the universality of the Latin language, it did not matter where we traveled, we could always attend and fully participate at Mass.