After asking about language options early in the install process, the installer then cleverly enables the aspell-en-gb package for me by default. Unfortunately, the system doesn't _use_ that dictionary - it still uses the en_US dictionary which is shipped as part of the aspell program package. It would be useful to have the installer create /usr/etc/aspell.conf with the appropriate language option, or possibly to have a UI for the installing user to select the system default from the installed dictionaries. cf. bug #37092.
Aspell needs to learn how to do the right thing most likely.
If you want to create files during install, that is an installer issue. That being said, the current version (0.33.5-1) tries to deduce what to do from the LANG variable.