I'm trying to override the normal portal language selection mechanism,
for various reasons we need to retrieve/enforce the client language
from a service other then the user registry. At the moment we have an
application object that retrieves the language, but I need to apply
that language so that the theme, and portlets honour that language as
the default and not apply the normal language logic.

I assume I have to do this in the theme, but I'm not sure how I would
go about it, anyone dealt with a similar issue?