This solution will allow you to set the Language of the Web Site when the Shopper is redirected to the Checkout pages. It is an alternate solution for Enhancement Request 129115.
1.Ensure that the Multi-Language feature is enabled in Setup>Company>Enable Features>Company tab>International section
2.In Setup>Site Builder>Setup Website>Appearance Tab>Languages subtab, ensure that the Languages you want your Web Site to be translated into are Online.
Use this URL:
c = is your Account Number
n = is theWeb Site ID (if you have Multiple Web Sites in NetSuite)
selshopperlanguage = is the language code