Why english?

Because English is so widely spoken, it has been referred to as a "global language". While English is not the 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 global 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 excludes those who, for one reason or another, are not fluent. It can also marginalise populations whose first language is not the global language, and lead to a cultural hegemony of the populations speaking the global language as a first language. Most of these arguments hold for any candidate for a global language, though the last two counter-arguments do not hold for languages not belonging to any ethnic group (like Esperanto).
A secondary concern with respect to the spread of global languages (English, Spanish, etc.) is the resulting disappearance of minority languages, often along with the cultures and religions that are primarily transmitted in those languages. English has been implicated in a number of historical and ongoing so-called "language deaths" and "linguicides" around the world, many of which have also led to the loss of cultural heritage. In the Americas, Native American nations have been most strongly affected by this phenomenon.

Taken from wikipedia^^v You can visit their site at http://en.wikipedia.org They got millions of articles in english about whatever. Do visit them as it will both improve your english and deepen your knowledge.