Nobody knows how many languages there are. The experts know there are thousands. The problem is: what is a "language"? What is a "dialect"? There are 7,000,000,000 human beings. One book says that most of those people speak one of about 30 languages. Some books say these are the six most widely spoken languages: English, Mandarin Chinese, Hindi/Urdu, Spanish, Russian / Belarusian, and Arabic. (Other books may have a different list.) Most people seem to feel that English is now the international language. It seems to be the language of the global economy; it seems to be the language of the World Wide Web.

I think english. But if you want to talk to people in countryside. You better to know the language of country.

Depending on how one differentiates between a dialect and a language, there are between 6,700 and 50,000 languages spoken in the world. (The joke is that a language is a dialect with an army and a navy.) English is by far the most influential language in the world today. See http://www.andaman.org/BOOK/reprints/weber/rep-weber.htm

English, but if you really want to integrate into a new community as Vasily has stated you should definitely learn the language of the country.