For package size reasons the Firefly Sung font to show Chinese characters in the statistics graphs 
is not included with LimeSurvey.

Please download it from http://sourceforge.jp/projects/sfnet_chinesepuppy/downloads/ChineseSupport/Fonts/fireflysung-1.3.0.tar.gz/ , 
unzip and put the fireflysung.tff file into the /fonts directory of your LimeSurvey installation.