I think the Peter Pan quote applies well here: “What if I fall? What if you fly?”
My sense of adventure and independence was very much encouraged by my parents, who obviously worried (especially on my 1st school ski trip age 9; in the 80's, no mobiles!).
A close friend was never allowed to go on these trips, she wasn't even allowed on school day trips. She hated not being included and resented her parents for it. Her mums anxiety was the reason.
A child demonstrating a desire to experience a different country and culture should be encouraged. It will benefit them enormously and a well-rounded, sensible, independent, adventurous and open minded adult will emerge from those expereinces.
As parents, we always fear for our children and nature plays a cruel trick on us when we have to switch from protector to mentor. We have to dig deep to do this, and the expectation is thrust upon us before we are ready and prepared for it.
There is a lot more to be gained than lost from an experience like this and OP, if your child wishes to go then I would try to find ways to dismantle your own fears. If you can do this, you will see that your fear will become excitement for them.
You will worry, of course you will, but there are ways to rationalise the fears and letting go a bit is something that you're going to have to do at some point, anyway - it's par for the course in parenting!
Maybe speaking to other parents whose children have taken part in the exchange or the teachers who organize it may help?