Office 2007 has a new, simplified design for deploying multiple languages. In Office 2007, elements that apply to all languages are grouped into one core package (MSI file). Language-specific elements are in other packages, one per application (e.g., Word, Excel, Outlook). This allows all language versions of Office (including English) to be deployed the same way. The core package cannot be deployed by itself. Setup combines the language-neutral core package with one or more language-specific packages.
If you are installing multiple languages of Office 2007, I highly recommend reading Simplified design for multiple languages in the 2007 Office system. This article discusses the customizations you need to make for installing a default language or specifying more than one language. It also provides links for installing Proofing Tools and adding languages after Office is installed.
– Andrea Weiss