How to translate and set default language?

You can translate it yourself by going to WHM -> RVglobalsoft Manager -> RVsitebuilder Manager -> Translation, select the Module and the Language you want to translate to.

Once you have finished it, you can force RVsitebuilder to display in the certain language by setting the default language at RVsitebuilder Manager -> Owner Configuration, and set the “Default Language” for Root’s users and Reseller.