Describe and compare the attempts to classify and label different kinds of speakers of English by Barbara Mayor and David Graddol. What are the problems and issues raised?

Many factors contribute to the gradual spread of any language: military, political, economic and religious. These factors affect the way in which speakers of other languages view its growth. It could be argued that the development of a single global language (English being the current main contender) would give its culture of origin unprecedented influence in world affairs, eroding the status of minority languages and threatening national identity….(short extract)