I think that you should use: VALUEOF(NQ_SESSION.session_variable)
And maybe in SQL results you should create something like that:
Select <presentation table>.<presentation column> from <subject area>
where <presentation table>.<presentationation column> = valueof(NQ_SESSION.<session variable>)
I have tried VALUEOF(NQ_SESSION.COUNTRY) as well but it doesn't work.
But I have noticed something even stranger - even when I don't have anything set for Default Selection option for this prompt, 'ENG' still gets automatically chosen when I enter the dashboard. How is that possible?