The Setup About box, which you get by clicking the About... button at any point in the Setup wizard, is intentionally kept in US English even for Setup versions that are localized (i.e., translated) into other languages.
The reason is that only US English language support is guaranteed to be available across all Windows versions (95 to XP, 2003) and all languages. Since the About box contains important technical support and contact information, this ensures that the information will be available under all circumstances, even if the customer is trying to run a localized Setup version on a system that doesn't fully support that particular localization.
Note - As described in Multilingual Setup topic in the online help, Setup excludes languages that are not supported on the customer's system. However, under some (rare) circumstances a language may appear to be supported by the system while in reality it is not, for example because not all fonts required for the language are properly installed.