download Vistalizator 2.30 if you want change display language in Windows editions other than (officially supported) Ultimate, like Starter, Home Basic, Home Premium and Business/Professional.

# Works in 32-bit and 64-bit Windows Vista/Windows 7
# Change Windows display language in less than 5 minutes! (Express installation mode)
# Uses official Microsoft Windows language packs
# You can install all 36 MUI languages and switch between them easily
# You can install 55 Vista LIP languages on top of specific MUI languages
# Compatible with Vista Service Pack 1 and Vista Service Pack 2
# User Account Control (UAC) compliant – prompts for administrative privileges
# Windows Speech Recognition works with all supported languages:
Chinese, English, French, German, Japanese and Spanish