You can maintain all the Languages as you like. Go to System > Languages.
Here you can see all the Language Lists.
To Add a New Language Click The Add New Language Button.
It will redirect you to a new page.
To Edit a Language Click The Edit from the language list Action options. It will redirect you to the edit page.
You can Translate Frontend and Backend Keywords from Language List Action Options. Click which keywords you want to set and it will redirect you to that page. You can write value for every keyword.