From a practical point of view it is probably good to have an international lingua franca, most likely a variation of English not only due to its current popularity but because it has accommodated a lot of simplifications [1,2] to make itself easier to learn. But for local cultures it would be an awful lot of work to translate centuries of tradition and literature into a global language, or a lot to lose by forgetting it. There is also a natural human tendency to modify and evolve the language that we use, while an international language has to be more stable or changes regulated lest it fragment as Latin did 1500 years ago.

1: http://en.wikipedia.org/wiki/Simplified_Technical_English

2: Contrast particularly major rivals French and Mandarin