Most likely its using even older installshield if there is no EngineVersion in setup.ini, check properties of setup.exe and from details tab "File version"
EDIT: I downloaded demo and extracted it, it's using installshield 6.31
So do this, download
winpack v3.00 beta
Run it and select "load packed file" and select/open data1.cab
Delete groups which have those other language files, demo was english only so there was only Group17: [any,en-GB] audioVisuals etc (deleting groups might take sometime.)
Finish pressing arrow button (Close current archive)
Now installing should work