What makes International English worthy of the "International" title, and not, say, British English, or American English?
Expressed simply, "International English" is an idea. It is "worthy" of the title because it is that version of English which is useful internationally. It represents those elements of the English language which are usefully learnt, as a second or additional language, by those, outside the zones where English is the (or an) official language. As such it is 'decentered' (or 'decentred' if you prefer). Attempts to create a version of English separate from the American or British "centres" include Basic Global English, based on a 750 word vocabulary, Basic English, Threshold Level English, and others. International English reaches toward cultural neutrality. According to this viewpoint, International English is a concept of English that minimises the aspects defined by either the colonial imperialism of Victorian Britain or the cultural imperialism of the 20th century United States. The International English Language Testing System, or IELTS, is an international standardized test of English language proficiency for non-native English language speakers. It is jointly managed by the British Council, IDP: IELTS Australia and Cambridge Assessment English, and was established in 1989.