For example, if you like to add simplified chinese
Copy resources/languages/en and rename a directory.
In this case you rename it into resources/languages/zhcn
Change CharacterTable in resources/languages/zhcn/Base.csv
CharacterTable,chinese
You can select from default, chinese, korean, thai
If your language doesn't exists or letters, add letters which is used to characterTable.txt
You can add and change a font by changing Font_Normal and Font_Bold in Base.csv
You now can change texts in resources/languages/zhcn/