I am running Emacs 23 and Aspell in a Debian Squeeze system. I've installed the aspell-hi package and spell checking of Hindi files works fine from the command line. I've set up aspell to replace ispell in emacs using the instructions here.
However, I can't find any way to make Emacs tell aspell to use the Hindi dictionary. Hindi does not appear in the list of dictionaries you get when you type M-x ispell-change-dictionary . If I just type in "hindi" I get "No match found." If I even try the crude method of saying (setq-default ispell-program-name "aspell -d hi") in my .emacs, I get an error that no such program is found.
I have searched extensively online but can't find any solution to the question of setting dictionaries in aspell in emacs, other than personal dictionaries and those listed by M-x ispell-change-dictionary.