OK, I also tried this with my XP Virtual Machine. I found out, that sLanguage is not the language of the windows. It's the setting of your Regional Options. But this doesn't really hurt.
Now, looking at Language\Default in XP shows 0409 too, which is right, because the Windows is in English. My Windows 7 says 0807, while in the list it says 0407 is German. It's possible, that after installing a MUI, the first two numbers of the value change from 04 to 08.
[Edit]At last it's working, but I need to know something. Is there any Wildcard option (*) in Construct?