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

I think we should learn English as lingua franca, since English is not our mother tongue, and it would be very difficult to learn it in a formal and perfect way. This doesn’t means that it is impossible to acquire perfect and formal English, but as time passes you could make your English seem perfect. To start is better the lingua franca because it is a way to communicate between people from different places in this world, and interchange different opinions and ideas. I think that English as lingua franca is more common in people, because many people have their English as a second or third language; so this makes it seem obvious that we would have less trouble learning English as lingua franca rather than the formal one.