I could go on and on, but I figure if the reader has bothered to read this far, I'm preaching to the converted, anyway. Those who have tackled other difficult languages have their own litany of horror stories, I'm sure. But I still feel reasonably confident in asserting that, for an average American, Chinese is significantly harder to learn than any of the other thirty or so major world languages that are usually studied formally at the university level (though Japanese in many ways comes close). Not too interesting for linguists, maybe, but something to consider if you've decided to better yourself by learning a foreign language, and you're thinking "Gee, Chinese looks kinda neat."
我还能再继续，不过我想如果亲爱的读者们能看到此处，多半他们早就已经同意我的看法。那些学习其他困难语言的人们有他们自己的恐怖故事，我敢肯定。但我仍然能相当自信地断言，对于一个普通美国人，中文比世界上三十多种主要语言（亦即在大学阶段常常学习的语言）中其他任何一种都难得多。这件事也许不会引起语言学家们的兴趣），但它值得你好好考虑一下，如果你决定最好学个外语，想着说“嗯～中文看起来好像不错。”

It's pretty hard to quantify a process as complex and multi-faceted as language-learning, but one simple metric is to simply estimate the time it takes to master the requisite language-learning skills. When you consider all the above-mentioned things a learner of Chinese has to acquire -- ability to use a dictionary, familiarity with two or three romanization methods, a grasp of principles involved in writing characters (both simplified and traditional) -- it adds up to an awful lot of down time while one is "learning to learn" Chinese.
要量化学习语言这样一个复杂而多层面的过程很难，不过一个量度是掌握必要的语言学习技能的时间。考虑到上述所有的中文学习者必须具备的东西，使用字典，熟悉两三种字母化方案，大致了解汉字系统（包括简繁），这加起来可是很多时间，而你仅仅是在学习如何学习中文。

How much harder is Chinese? Again, I'll use French as my canonical "easy language". This is a very rough and intuitive estimate, but I would say that it takes about three times as long to reach a level of comfortable fluency in speaking, reading, and writing Chinese as it takes to reach a comparable level in French. An average American could probably become reasonably fluent in two Romance languages in the time it would take them to reach the same level in Chinese.
中文本身要更难多少呢？再次我使用法语作为简单语言的例子。非常粗略和直觉的估计，不过我想说要达到法语中类似的读写流利程度，中文需要你三倍的时间。同样的时间，一个普通美国人多半可以学会流利使用两种拉丁语系的语言。

One could perhaps view learning languages as being similar to learning musical instruments. Despite the esoteric glories of the harmonica literature, it's probably safe to say that the piano is a lot harder and more time-consuming to learn. To extend the analogy, there is also the fact that we are all virtuosos on at least one "instrument" (namely, our native language), and learning instruments from the same family is easier than embarking on a completely different instrument. A Spanish person learning Portuguese is comparable to a violinist taking up the viola, whereas an American learning Chinese is more like a rock guitarist trying to learn to play an elaborate 30-stop three-manual pipe organ.
学习语言也许类似于学习乐器。比如说，虽然口琴有某些精彩的作品，一般而言钢琴学起来要比其他乐器困难而花更多时间。作为类比，可以说我们都是某种乐器的高超演奏家（即我们的母语），而学习同类的乐器则比学习完全不同的乐器容易得多。西班牙人学葡萄牙语类似于小提琴手学习中提琴，而美国人学习中文则更像摇滚吉他手试图学习演奏拥有三个手键盘，三十个音栓的管风琴。

Someone once said that learning Chinese is "a five-year lesson in humility". I used to think this meant that at the end of five years you will have mastered Chinese and learned humility along the way. However, now having studied Chinese for over six years, I have concluded that actually the phrase means that after five years your Chinese will still be abysmal, but at least you will have thoroughly learned humility.
有人说过学习中文是“五年关于谦虚和低调的课程”。我曾经以为这是说五年之后你就能掌握中文，同时学会了谦虚。然而，我现在学习了中文六年，我的结论是，这句话告诉你五年之后中文对你来说仍然是神秘的深渊，不过至少你已经彻头彻尾地学会了低调这个好品质。