Just got here and missed all the fun.
You've got a pretty good explanation now.
I too think Mozart's setting is one of the most delicious short bits of choral music there is.
Funny thing about Latin being economical... this seems to be one of the most devilishly difficult texts to translate well, especially in a meter that fits the original. All of the "translations" I have seen have either been way off the point, or heinously tortured English. And I can't do any better.
My current church choir director seems to resist singing in Latin for doctrinal reasons, but you can't beat it for a singin' language!
=Glenn