In Swedish I pronounce y as y. It has its own sound and doesn’t sound like another letter, so it can’t be written as a combination of other letters.

Üpsilon

In Flanders (at least where I’m at) we usually say I grec, but when doing math or reciting the alphabet, we say IJ.

Usually same as our compound letter “ij”, similar but not quite how you’d prononuce the word “eye”. Less commonly it’s pronounced as “i-grec” (greek i) or “ypsilon”.

Sound like igrek.