Additional display languages on Windows Server 2008 R2: Error while installing

I am running a Windows Server 2008 R2. I would like to install italian as another display language, so I downloaded the Multilingual User Interface iso file with a lot of locale packages included. However, when I try to install the language pack (Install/Uninstall display languages) I see the following screen telling me that the languages cannot be installed:

UPDATE: We are using volume licensed software and we have only the single language system, so there is no way to have multiple languages. However, is there a way that I can change the system language? I dont need english.

There are two types of language packs.

One is the 100% translation pack, these require specific licenses. I believe a Volume License, with the restriction that the language you are trying to install is not priced higher than the language you bought.

Then there are the Language Interface Pack (LIP). The LIP contains only a subset of resources required for a specific language, no license is required.

Understanding Multilingual Deployments