Do a websearch for Language Courses Abroad and you will find lots. I looked for one recently for my teenage son, and actually found that the majority listed are for adults, not teenagers. Sorry I can't recommend anything specific, but it's a start.
I did a spanish course in Santiago de Compostela at the university one summer and it was really cool I met a lot of nice people and its quite adult orientated, and they have activities like pilgrimages as its a very relgios part of Spain.
You could look up the Open University - I think you can do specific courses that are base abroad with them. You don't have to do a whole degree (I think).