Here's a more accurate list: http://technogadgetworld.blogspot.com/2013/06/top-10-most-spoken-languages-in-world.html

To xiaokaoy:

The reason the number of Hindi speakers isn't higher is because, despite India being the second-most populous country, Hindi is only spoken by a specific region of Indians (mostly the north central area, iirc). It's the most prevalent of the Indian languages because of its presence in the major cities, but there are many dozens of other Indian languages interspersed in the country. Imagine if every different state in the U.S. spoke a completely different language instead of all speaking English, and that's sorta what's going on in India.

Mandarin, in comparison, has a stranglehold on a vast geographical area in China due to the long history of successful interregional conquests by Mandarin speakers, hence why most Chinese citizens speak it.

Nowadays the population of Brazil is more than 191 million, considering the other countries where portuguese is spoken, I think portugese language is about 250 million of native speakers.

I think your list is more accurate than link from Polyglotunraveled, because malay-Indonesian is the national language of Indonesia, Malaysia, and Brunei. Population of Indonesia is 248million and almost all Indonesians can speak Indonesian language.

I'm thinking Hindi is number three because of the population but it is interesting to note that it is not one of the official languages of the United Nations. The six UN offical languages are Spanish, English, French, Chinese, Arabic, and Russian, of which UN documents are written.