Mandarin is the national language of China and Chinese is the most widely spoken language in the world. By learning Mandarin you will be able to speak with more people than any other language- including English. Mandarin is a tonal language. Words must be spoken at the right pitch to convey the correct meaning or be understood. Many Mandarin sounds are different than those of Western languages.
Mandarin is comparatively spoken by fewer non-Chinese than most European languages spoken by non-natives of their respective countries. That means there is a greater demand for Chinese since fewer Westerners are able to speak it.
China is rapidly becoming a world economic power as it opens its doors to foreign investment and expands its infrastructure. Those who know Chinese it will be valuable for them in business. The Chinese population is rapidly expanding its online presence. It will become increasingly useful for online communication.