Why do we need a global language
Please think deeply why do we need languages primarily instead of why do we need a global language . Do English ancestors create language to represent themselves? Do they mean to create a culture icon for later generations? Absolutely not, they created language to communicate with people within their community---share ideas through language in essence with people surrounding. And so do people live far away from English people at the moment, such as Chinese, thus Mandarin came into being.
With the development of society, an increasing number of cooperation about economy, politics and culture are needed. The chief international forum for political communication--the United Nations, and international academic and business communities were established . So the culture and ideas need to exchange. The growth in international contacts has been largely the result of inter-lingual and cross-cultural. In order to communicate with foreign people, translation came.
Translation has played a central role in international stage, there would invariably be interpreters present. But there are limits to what can done in this way. In communities where there are many languages in contact, such a natural solution does not readily apply. A conversation over the Internet between academic physicists in Sweden, Italy, and India would not be impossible, if each plugged in to a 3-way translation support system, but it would be far more complicated than the alternative, which is for each to make use of the same language, only if a common language is available. And we all know that translation costs are really expensive , half of the budget of an international organization can easily get swallowed up in translation costs.
The availability of both these facilities , provided the circumstances needed for a global language to grow.