Howto use build in languages?

[Blinkiz]

Just started to use Zimbra 5.0.9 and would like to change default language for all users. I can see that my preferred language should be included in Zimbra.

On Zimbra Website - Languages I can read,

Each ZCS Open Source and Network Edition ships with English enabled by default. Administrators can easily change the default language by setting new default for a given Class of Service (CoS). End-users can override any default language settings and choose their own simply by changing their language preferences.

So I should be able to change language under "Configuration", "Class of Service" and then "default". Problem is that I can't find where to change language. Where can I change the default language for all users?