My first point was that if you usually speak German or some such language, learning Spanish is just one more language while Mandarin equals learning three new languages: Written characters, spoken Mandarin, and Pinyin Romanization.
Reading Spanish tells you directly how to pronounce it. You talk internally while you read, training two things (that are basically just one) simultaneously. I went to Mexico only a few times yet picked up a lot of Spanish, even when just wandering about and looking at traffic signs and advertising.
English pronunciation already often differs from what is written, so English as a foreign language is not easy; it also has a very large vocabulary. In Mandarin however, writing and speaking are totally disconnected – they are really two different languages to learn. Walking around town, wandering through supermarkets looking at signs and labels teaches you nothing. You cannot pick it up like you pick up Spanish while rollerblading drunk through LA. Learning Chinese is work.
Moreover, these two, speaking and writing, need a third one, so called Pinyin, to connect them.
Pinyin is pronounced somewhat like English (see the "ai" on the picture - which seems no longer available in 2016), the main difference being the four tone marks. 我饿( = I am hungry) is for example “Wo\/ e\”. “\/” is here the “caron” diacritical mark and “\” the "grave" one. Although the text browser here may get these marks right, many internet browsers do not, so I just use / and \.
Chinese pupils learn Pinyin while learning Chinese in school. They do not do this to prepare for English. They learn this Western bit of language in order to deal with their own language, to sort stuff in a dictionary or encyclopedia for example. Chinese still sometimes order according to stroke counts and suchlike, also to find entries in older versions of dictionaries or to input text messages into phones, but that needs dedicated input software.
Imagine we needed to learn Chinese characters to deal just with English. Regarding this aspect, Chinese is not an efficient language. Pinyin is the beginning of an eventual complete Romanization of Mandarin, just like it happened to Vietnamese. Next time ...[Series discontinued for lack of interest]