[arnvald]

I'd be really surprised if Mandarin reached such status not only in 20 years, but in the next 100 years. While it certainly gets more popular due to China's growth as an economic power, its far behind English when it comes to number of non-native speakers.

On top of that, learning Mandarin is very difficult. It's a tonal language - as someone who has absolutely no ear for music, I find it challenging to understand the differences between different tones. The alphabet is another obstacle - even in China children at school learn words written in pinyin (system of writing Chinese characters in Latin alphabet) first. Even with China becoming an economic world leader, I don't see Mandarin becoming mainstream (having said that, I learn it and I enjoy it, although it takes me much, much longer than to learn any other European language)