We need to communicate, and the means for this is language. Sometimes we need specialised jargon to talk in a particular forum, and sometimes we need alternates (or adjuncts) to help. For example, it’s useful to have a mathematical notation; and its use extends far beyond the reaches of pure mathematics itself. We need pictures to express ideas, and some disciplines, such as music, need their own notation. All of this is complicated by the existence of well over 7,000 languages worldwide. I’m lucky, and have English as my mother tongue. English seems to be a useful default language, but let’s not forget that 300 languages are spoken in the UK alone (this figure is from the Internet, and I’ve no reason to argue). But it’s hard to argue that it isn’t useful for people to share a common language of communication.