I was thinking more about elementary education. I also excluded exchange students since they probably don't take the test. You are right. It could be helpful in

I was thinking more about elementary education. I also excluded exchange students since they probably don't take the test. You are right. It could be helpful in other ways, but probably not in the scoring of PISA. I would assume that learning won't get any easier when you don't know the language. If you get bad start early on, it can hurt you later on or even frustrade you. So even it might be small aspect, it seems that PISA-test rewards for homogenous.