1. English
2. Mandarin
3. Spanish
4. French
5. Arabic
6. Hindi
7. Russian
8. Portuguese
9. Bengali
10. Malay
Resources
First language speakers The World Factbook
Number of first language speakers Ethnologue
Continents spoken on The World Factbook
Countries spoken in Ethnologue
Used by UN The World Factbook [The UN uses six languages amounting to more than 50% of the population's first or second language]
Number of weeks to gain basic proficiency Foreign Service Institute – U.S. Department of State [for a native English-speaker]
I've got my ticket Google Translate