Installing a new language pack for Exchange Unified messaging is pretty easy. In addition to the default English US there are a number additional language packs on the installation media.
The following files are in the \UM directory on the media.
Each of these MSI files is a language pack. These are also available for download from Microsoft.
Once you have your language pack you need to install it onto each Exchange UM server you want the language pack available on.
This is done by running the setup command on the CD. The command format is:
Setup.com /AddUmLanguagePack:xx-YY /s:<path to language pack>
where xx-YY is the language you want to install, which is in the name of the MSI file. For example I used the command below to install the Australian English on my Exchange UM server.