Mandarin Chinese - 882 million users
Spanish - 325 million users
Arabic - 206-422 million users
Hindi - 181 million users
Portuguese - 178 million users
Bengali - 173 million users
Russian - 146 million users
Japanese - 128 million users
French - over 100 million users
German - 96 million users
Italian - 85 million users
Norwegian - about 20 million
American Sign Language - perhaps 2 million US users
None of the above; English is enough of a challenge for me.