This is a list of the Supported Languages (as per our Installer Behavior Wiki entry):
en - English
ja - Japanese
de - German
es - Spanish
fr - French
nl - Dutch
pt - Portuguese (Brazil)
These are the languages available when bulk importing users via CSV in the Language Code column. The list of languages in the Configuration menu under Language Preference are those available for Content Translation and are a separate configuration.
If you reference this Wiki entry you'll see this feature described as such: "Content Translation allows the system to provide User Entered reporting content across multiple languages by allowing users to translate content such as Report Names, Column Titles, Chart Labels, etc."
As such, that list of languages refers specifically to Content Translation functionality, not that each is available to apply globally everywhere in the application - i.e., Page Names, Welcome page, Navigation Bar, etc.