Hi Juliette! As far as I know volunteers only get transferred if there is a case of illness or cancelation, and only if it otherwise means that a certain class doesn't have a teacher. When I was volunteering I did not see anyone transferred, they are very well organized and try to accommodate everyone's wishes.
Hi Rowan, From my experience I can tell you that during your classes you can pick up a lot of Indonesian very quickly. If you want to go more into debt you can always follow an extra course which can be found easily.
Ubud!