It's EXACTLY English. After that i think Germany and Chinese. They are my top 3. After all it depends on which country we are talking about but English would never change.^^

@Hasan Zaidi: 

1. Thank you for introducing me to ICFE.

2. I was thinking of GLOBISH (global + English):

a. It has 1,500 words and phrases.

b. Supposedly, a business person who knows Globish can negotiate in English with an English-speaking business person.

c. People who learn only Globish are NOT interested in becoming fluent in English. They have only one goal: to sign the business deal!

3. If you google "Globish," you will find many results.

undoubtedly, English...

James are you referring to ICFE by Cambridge?

Fatih:

I think that everyone agrees that English is the international language in almost all aspects of life, including international trade and finance.

In fact, there is a special kind of English (I cannot remember its name) that has been invented for business people. It is  for business people who want to learn English ONLY  for  one reason: to speak and understand  enough English  in order to conduct business.