Before you consider adding support for Aspell, first make sure that someone else has not already done it. A good number of dictionaries off the Aspell home page at http://aspell.net. If your language is not listed above feel free to send mail to aspell-dict at gnu org for help in getting started.
Adding a language to Aspell is fairly straightforward. You basically need to create the language data file, and compile a new word list.