[simongray]

There's no chance that Mandarin will ever take the position of English and that statement is solely based on the peculiarities of the written language, not even the seeming lack of interesting content produced in Mandarin (comparatively tiny Korea and Japan are much bigger cultural exporters than China and Taiwan).

Chinese is only really spoken in any capacity as a second language in countries that used to use Chinese or Chinese characters for the written language (Korea, Japan, Vietnam) and countries where ethnic Chinese people currently live. If you did not grow up looking at Chinese characters and speaking a language that has a big lexical overlap with Chinese (Korean, Japanese, Vietnamese) then Chinese is extremely difficult to learn. The writing system is incredibly impractical since it requires learning thousands of symbols to read any normal piece of text and the lack of spaces makes parsing many basic sentencse very challenging until the learner is at a very high level (must know all characters in sentence, must know most words in sentence, must know general grammatical flow in sentence).

The coming of electronic dictionaries and Pinyin IMEs has made it much easier to learn Chinese than it used to be, but it is still ridiculously challenging. Many learners living in China simply skip learning how to read, which I don't think happens with many other languages. Chinese people are often functionally illiterate and even educated Chinese have trouble reading certain things (names, especially). There's a very well-known essay in the Sinologist community about all of these challenges: http://pinyin.info/readings/texts/moser.html