how to internationalizate an application?

hello,

I'm making an application (app). This app must support multiple languages ( for example chinese, arabic, etc.)

The app have a menu. In this menu you can select the language. When you select a language, the app read a determinated xml file with translated fileds ( for eaxmple, the file "lang_chinese.xml" ) and overwrite the visual text of the app.

My conceptual dudes are about: fonts.ttf VS codecs. I don't know how to use in xml file, if I require fonts in chinese, or Helvetica font already have chinese symbols but i don't see it, because i don't use the determinated codec... I'm searching in www but i don't found the information..

Thanks in advance