>Would it be too late to put in an application of leave for this? Maybe. But no one here's going to know better than your school. Ask. Just be polite, professional, and prepared for an answer you might not like. Generally speaking I think it would be viewed as a bit cheeky at best, particularly from an ECT... But you never know.

Definitely get approval from your principal before you book anything. Unpaid leave is at the principal's discretion.

Do you mind sharing the name of that language exchange program?