What should we learn, English as a lingua franca or "formal" English?

I think that even though English has borrowed a great force and in various parts of the world is very necessary to have a good job, better education and greater opportunities generally think it is important that each country has a great diversity and between the characteristics of this diversity is the language, which must be respected, and if English is implemented as "formal" could lose this diversity of languages has, as they may be forgotten the other existing languages. So in my opinion, English should continue as the choice of second or third language, so that there is a balance between the mother tongue and second or third language (in this case English).