Green Desktiny comes with English as a default language.
However, to edit and add new language is very simple.
Go to menu
Admin->Languages and choose Add Language.
You can see the interface as below.

For example, we add Dutch into our helpdesk.
Tinymce Lang is language used for Tinymce HTML Editor, we can find these languages in greendesktiny/js/tiny_mce/langs/
Just add the file name into textbox without the extension.
Directory Lang is a folder created that contain your languages. You must edit these files.
Locale is a set of preference information related to its environment/cultural conventions, e.g. date format.
You can add more than one locale since some platforms of webhostings may vary with others.
As English is the default language, every time you add language it is still in English.
You have to translate it into your language. The files you have to translate is exist in the directory where you have added new language. (e.g.
lang/nl/)
When you like in full Dutch, you can go to menu Admin->General Setting.
Change the
Default Front Language into Dutch.
Change Yes to
Front Multilingual Disabled.