This article applies to the 123-reg InstantSite package.
This article will explain how you can change the interface language on your InstantSite.
Scroll down to the Create your website section and click on the InstantSite icon.
Click on the Login button next to the relevant InstantSite package.
Click on the Pages link.
Select the language from the drop down menu in the bottom left.
Click on the Save changes button.