As you might be aware of, the SCSM 2012 Self-Service Portal is multi-language capable. However, although you can add languages to the portal, I haven’t found any documented steps as to how to change the default language (which is always set to English).
This blog post will walk you through the necessary steps to change the default language of the SCSM 2012 Self-Service Portal.
Dieter Gasser's blog 