qstardict is looking for dictionaries in two folders as default.
Those folders are "/usr/share/stardict/dic" and "~/.stardict/dic".

The first folder is available for all users.
The second folder is in the home directory and available for particular users only.

You have to create one of those folders if it does not exist and put all your dictionaries here.

It is also possible from the configuration dialog to add or remove a folder from lookup by pressing
"configure plugin" button beside "stardict" plugin.