Because English is so widely spoken, it has been referred to as a «global language». While English is not an official language in many countries, it is the language most often taught as a second language around the world. It is also, by international treaty, the official language for aircraft/airport communication. Its widespread acceptance as a first or second language is the main indication of its worldwide status.
There are numerous arguments for and against English as a global language. On one hand, having a global language aids in communication and in pooling information (for example, in the scientific community). On the other hand, it leaves out those who, for one reason or another, are not fluent in the global language. It can also lead to a cultural hegemony of the populations speaking the global language as a first language.
A secondary concern with respect to the spread of global languages (including major languages other than English such as Spanish, Chinese, Arabic, etc.) is the resulting disappearance of minority languages, often along with the cultures and religions that are primarily transmitted in those languages. Language death caused by English has been particularly pronounced in areas such as Australia and North America where speakers of indigenous languages have been displaced or absorbed by speakers of English in the process of colonization. The expansiveness of the British and the Americans has spread English throughout the globe.
The major varieties of English in most cases contain several sub varieties, such as Cockney slang within British English, Newfoundland English, and the English spoken by Anglo-Quebecers within Canadian English, and African-American English within American English. English is considered a language with no variety being clearly considered the only standard. Because of English’s wide use as a second language, English speakers can have many different accents, which may identify the speaker’s native dialect or language.
Just as English itself has borrowed words from many different languages over its history, English words now appear in a great many languages around the world, indicative of the technological and cultural influence of English speakers. Several languages have formed on an English base – Tok Pisin was originally one such example. There are a number of words in English coined to describe forms of particular non-English languages that contain a very high proportion of English words – Franglais, for example, is used to describe French with a very high English content (spoken mostly in the border bilingual regions of Quebec).
StArt Linguistics 
To tell the truth, I don’t see much point in looking for arguments for or against English as a global language. The situation is, probably, out of anybody’s control. But there is another issue we, as English teachers, should consider and might have a say in.
Becoming a global language, English is changing. A simplified version is used in cross-cultural context. The question is whether we should teach it to our students adopting a non-native model as our target, or try to be as close to native speakers, both in our speech and communicative behaviour, as possible.
Who knows – our decision in this matter might influence the future of English as a global language.
Just in the Greek and Roman Empires and all of that Greek was the most widely spoken and understood language. So, French used to be the language of diplomats. German was the language of railroads and transportation. So, why not have English as the “Global Language”? Thank you..