OK dear Solid.Chen ,there is a hack but it's a bad solution since it modifies the core with no garantee that is will be possible to get the functionnality with the next versions
1 ) open qa-include/app/admin.php
duplicate the first function qa_admin_check_privileges and rename the copy qa_admin_check_privileges2.
In the copy , change QA_USER_LEVEL_ADMIN by QA_USER_LEVEL_EXPERT
2 ) open qa-include/pages/admin/admin-categories.php
on line 47 , change
if (!qa_admin_check_privileges($qa_content))
by
if (!qa_admin_check_privileges2($qa_content))
3 ) go the "admin pages" page and add the link to categories only accessible to experts and higher
use the link admin/categories ( = the admin link for categories )
tested with admin , expert and normal user :)
edit : QA_USER_LEVEL_EXPERT or anyone from this explicit official list :
QA_USER_LEVEL_BASIC
QA_USER_LEVEL_APPROVED
QA_USER_LEVEL_EXPERT
QA_USER_LEVEL_EDITOR
QA_USER_LEVEL_MODERATOR
QA_USER_LEVEL_ADMIN
QA_USER_LEVEL_SUPER