language did not disappear it is still there, however it is lack of the chinese character encoding (symbols) within specific font you are using, that phone tries to read but is not able to display as it is not there. (this will not damage your phone, just go back to english language or get another font or go back to original sony ericcson font)
to check if the font you want to use, has character encoding for other languages than english, open the font with windows CHARACTER MAP program as look for sumbols that you have in your language.
character map is located under PROGRAMS---ACCESSORIES--SYSTEM TOOLS---CHARACTER MAP
easiest way to figure which font has character encoding other than english is by its file size. generally fonts larger than 150kb will contain other languages characters.