Where can I get a combination language immersion / hiking experience in South America?

I’d contact Adventure Travel http://www.adventuretravel.com/, or any other similar organization (a search for adventure travel will bring up a large number of options). They could offer the hiking experiences you are looking for. Some of these outfits will even tailor an experience for you. Perhaps they could find a Spanish speaking guide for you, or put you in touch with a guide service that offers services to Spanish speaking people. Often they will have you stay in homes of residents, rather than in hotels.

Your experience will depend largely on the company you choose, so check them out thoroughly (how long they have been in the area, experience of the guide, reputation, fiscal history, etc.). Expect to pay big bucks, especially if they tailor an adventure for you.

Go and volunteer in Costa Rica.

My nephew did an intensive Spanish language program in Costa Rica and loved it.

You just gave me a great idea. I have been looking for a church. I think I’ll kill two birds with one stone, and hike over to the spanish church up the street on Sundays and see if they’ll have me.