In The Alchemist, the language of the world refers to the oneness of all things: that the universe is tied together. During the 1960s this idea came into prominence with the belief that the damage we did to the world would damage those living in it, which has been proven with studies about pollution, etc. This is not a new concept: writers in England and the United States responded in the same way with the advent of the Industrial Revolution and its damaging effects to the environment many years ago.
Because we are all connected, according to Coelho, we are not only made of the same "stuff," but we can communicate with nature if, as Santiago tells the Englishman, we "listen" to nature speaking to us. In this regard, we should also, then, be able to speak to one another regardless of where we come from, which Santiago discovers in being able to understand people who do not speak his "native" language.
Based on this assumption, Santiago tells the Englishman that by speaking the language of the world, nature will help us as we move about the world—in their case, by allowing them to successfully navigate the desert with the caravan. The universal language is something that, as seen in the book, is something that many people know about (like the gypsy, the alchemis, the King of Salem,etc.), but others (like the Englishman) do not. Believers feel the language links people to the world and to each other. This is my "take" on the language of the world.
When we're presented with opportunities, we must find the courage to pursue them. It's a pretty obvious point, really; and this is text offers nothing fresh or extraordinary in the way of helping one achieve one's goals. As accessteacher said, this is a typical self-help book which uses the metaphor "language of the world" in an attempt to offer a fresh perspective on an overused theme.
As a typical self-help book, this novel is centred on the quest for self-enlightenment and realising where our "treasure" is. The "language of the world" can be translated as the opportunities that are open to us and the life we are able to live, however, the only way we can understand and grasp those opportunities fully is with courage - we need to have the "get up and go" to be able to make ourselves open to these opportunities.
The Alchemist is mostly about taking risks so that one can find his/her true path in life. Santiago sets out on a journey to find himself, but along the way, he is faced with a series of obstacles. He must have the courage to accept what life offers him so that he can reap the benefits of his experiences. So, "the language of the world" has to do with accepting the risks and opportunities offered in life.