File Name 
File names are based on ISO 3166 codes of countries. 

If want to create a new language file with your laungage, please go to: 
http://nl.ijs.si/gnusl/cee/std/ISO_3166.html 
and find your laungage's 2-letter code listed under "A2". 
Name your file "lang_"+"the code"+".php" 

Examples: 
China : lang_cn.php 
Germany : lang_de.php 
France : lang_fr.php 
Japan : lang_ja.php 
Korea : lang_kr.php 
Russia : lang_ru.php