English is a plastic and fluid laguage, ever changing that is defined by usage. If English speakers invent or borrow a word or expression, it is officially English and not "slang". The experts on the English language such as Oxford University or Merriam-Webster are mere chronicallers who collect new words and expressions, constantly. In 2014, there were 1,025,109 known English words and that number grows every year. We do not have an Academy of English, telling us what is English... how to speak ... what to think. Ironically, the lingua franca of the planet is currently English. French is just too limiting, constricted, controlled to have led to the explosion of creativity of the English speaking world over the last few centuries. French tongues and minds are constrained in an Académie française straight jacket.
Not entirely accurate. unofficial French exists too, just like unofficial English. However, the Academie allows for the existence of an official French. I remember participating at a small conference in China. One speaker was Cameroonian, one Australian, one Pakistani, and me as the token Canadian. The rest were Chinese.
Interpretation completely broke down since the Chinese-English interpreter had learnt only US and UK English. She could undertand my English since Canadian is somewhat close to these other two, and she got some of the Australian, but was at a complete loss otherwise.
Ironically, a Chinese Esperanto-speaking friend of mine and I jumped in to save the day. Esperanto like French has a standard international form. One big difference between Esperanto and French is that Esperanto is multiple times easier to learn. But one similarity is that they both benefit from a language accademy that ensure the existence of an international norm. English has no international norm. In fact, according to one study, 15% of fatal air crashes are caused by linguistic misunderstandings.
So the existence of a standardized international variety of a language is not a disadvantage at all. On the contrary, it's an advantage to international communication.