Line spacing in multi-language layout with Core Text

Similarly to the space between each letter in European languages, Chinese writing uses a narrow space between characters, though it does not observe the equivalent to the wider space between words, except in rare occasions. (In this respect, it may somewhat resemble a form of scriptio continua.) When space is used, it is also fullwidth. One instance of its usage is as an honorific marker. A modern example in Taiwan, is found in the reference to Chiang Kai-shek as 先總統　蔣公 (Former President, Lord Chiang), in which the preceding space serves as an honorific marker for 蔣公. This use is also still current in very formal letters or other old-style documents. When Chinese is written in transliterated form (as in Hanyu Pinyin), spaces are used to assist in reading. source:http://en.wikipedia.org/wiki/Chinese_punctuation

So its because in chinese as space is used a bit differently than in english.