It's not hidden

The question of how a language is learned has been studied for several millennia.  It's an ancient question.  For that reason it ought to be clear what the process is for learning a new language.  But, that is not the case.  Well, if you believe Rosetta Stone, you think it's clear (or Berlitz, Pimsleur, Living Language, or the name of a 100 other companies).

But if it's true that a person can learn a language in a matter of a few months rather easily, then when I look around at all the countries of the world, I should see a great number of bilingual, trilingual people.  I do see a few pockets of proof of this theory.  Swiss denizens, South African, Ukranian, and a few others do learn 2 or more languages just from growing up in a multilingual environment.  But most people in the world don't.  Why not? It's so easy, right?

Upon further study by modern scholars, variables enter into the equation when learning a language.  One's age when learning a language, for example, yields different results.  One's purpose for learning matters.  The method used sometimes facilitates or impedes learning a language.  Other factors also enter into the picture, such as educational background, opportunity for use, and societal status of each language.  All these factors should make the learning process transparent and easy because methods could and have been made to take into account all of the factors affecting language learning.

But, even if there were a hundred factors in learning language, it should be easy by now, given the thousands of years people have been learning and speaking other languages. Modern people have left it to the schools rather than language scientists to teach languages to people. The schools have used various models for teaching languages, but it still takes place in an artificial environment with the accompaniment of textbooks.  In light of all the years of practice and all the years of research, schools have not changed their approach, regardless of model.  In addition, businesses which have specialized in training people in language have adopted the schools' various models as their approaches.

Evidently, these models are flawed.  It's still a daunting task to learn a language. The research has been done, however, and the process is a known process.  It's not hidden.  It's just that foreign language departments, schools, and businesses are not listening or looking to the available language science.  Wouldn't it be nice for people of nations to speak to each other regardless of language.  They could.  Easily. So be it.