A little while ago I had a wonderful discussion with Michael Ernst, professor at University of Washington. Among other things, he mentioned that his wife has a PhD in second language acquisition. In this discussion I learned about the concept of environmental learning.
I realized, that the concept applies in our case. Zeeguu is aiming exactly at this: "accelerating environmental learning" by "intercepting" every interaction with the new words in the environment in which the learner is embedded (which can be virtual though, like an eBook or the Web), providing translations, and automatically updating the model that represents a users "degree of knowledge model".
Evidently, before the user is ready for environmental learning, he needs to get a good basic grasp of the language. Probably a vocabulary of 1000 words or so (although this remains to be decided by future research). For this, intensive language courses, or applications like DuoLingo are very useful.
N.B. Note that the concept of environmental learning is quite broad, and it can be discussed also in the context of "the classroom environment" it seems (e.g. this article)
