ispell-local-dictionary-alist

ispell-local-dictionary-alist is a variable defined in `ispell.el'.
Its value is

nil

Documentation:
List of local or customized dictionary definitions.
These can override the values in `ispell-dictionary-alist'.

To make permanent changes to your dictionary definitions, you
will need to make your changes in this variable, save, and then
re-start Emacs.

You can customize this variable.