中文是一种文字，中国人都用它写字。汉语是一种语言，中国人说的语言，写出来就是中文。This is my personal understanding. i'm not sure if u will get it.

中文 literally means languages spoken by Chinese people, which in theory includes other languages spoken by ehnic minorities in China such as Tibetan language, Mongolian languages and so on. 汉语 literally means languages spoken by Han (most people in Chinese are Han). In fact, 中文 and 汉语 are the same. But 汉语 tends to be more accurate in describing Chinese language. I my self perfer to say 汉语 instead of 中文 when communicating with foreign friends.

首先，我想先从“中文”的“中”和“汉语”的“汉”这两个字解释。“中文”是针对外国的语言来说的，意为“中国的文字”；而“汉语”是区别于中国国内其他语言来说的，中国是有56个民族的国家，汉族的人数最多，其他民族的人统称为“少数民族”所以中国国内不仅有汉语，而且还有藏语、维语、朝鲜语等其它少数民族语言，但是中国主要使用的语言就是汉族人使用的汉语，也是全国通用的法定语言，所以其他少数民族地区的人不仅用自己民族的语言而且也学习使用汉语。 其次，我再从“文”和“语”这两个方面解释。顾名思义，“文”意为“文字”，指的是书写出来的文字，“语”意为“语言”，指的是说出来的语言，所以从这个角度讲的话，“中文”和“汉语”的区别就相当于“英文”和“英语”的区别。

They're the same. 汉语or中文 is the language of the Han nationality, the majority nation in China.

" Mandarin " is called different names by the Chinese living in different places. " 中文" is called in Chinese Mainland, Taiwan, Hongkong and Overseas Chinese communities; while " 汉语 " is only called in Chinese Mainland. For example, HSK is 汉语水平考试（hàn yǔ shuǐ píng kǎo shì）.