Partially translated Windows 7 languages packs display “The Remaining UI", that part of Windows 7 which most users won’t ever see, in a base language. Dutch, English, French, German, Italian, Japanese and Spanish are fully localized and thus have no base language.
More information about the extent of localization (EOL) and the difference between Language Packs and Interface Packs can be found in our articles Understanding Windows 7 Language Packs: Introduction and Architecture and Windows 7 Language Packs Details and Availability.
Windows 7 Language Pack Installation
1. Start -> All Programs --> Windows Update --> Optional Updates.
2. Open optional Updates and go to the section Windows 7 Language Packs. The process is depicted on a RC Windows 7 so please ignore any references to Release Candidate.
3. Tick the Language Pack you want and hit OK
4. Proceed with Install Updates
5. Depiction of Windows 7 downloading a Language Pack
6. Automatic install initiated after download
Change the display language as explained in the next section