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

I think that all the people need to learn more the Formal English that as a Lingua Franca, because if you learn the formal English, it will open more opportunities in your life, because now in our times the English is a global language and is used in the most of the countries around the world. One big profit of learning formal English is that it will give you the possibility to enter into a multinational company, and it will give more opportunities to get a great job with good benefits and wages.  The Formal English will serve you more because is most likely that in great companies as the multinational, you will need to travel a lot, or use a plenty English a lot. So I think that learning formal English will open you a lot more opportunities in your life.