I have a system (Dell laptop) with an English Windows 7 Pro on it.
Furthermore, it has Java installed (JDK6).
In a build process, the Flex compiler (compc, Flex 3.3) is called (from ANT). It produces German error messages. Why would it do that? The same code with the same ANT build scripts works in English on all other systems in the company.
The language for the compiler messages is apparently determined by the language/country selected at Control Panel → Region and Language → Formats → Format
Other hits around the web indicate the “Language for non-Unicode programs”, but at least for Java6 x64, that doesn’t apply.