Hi rajthayi,
in my opinion the easiest way to do this (and I have tried it by myself ;-)): You can extract your files and manually edit them. In the manifest.xsf file, you will find an <xsf:scripts> tag. Remove this and you will be able to select another language.
You might want to clean up the .js files too, but you don't have to.
HTH,
Karsten