It's not easy but if feasible it would be just *great*.
My locale, in example, is pt_BR. When I install some application which depend directly or indirectly on aspell (or ispell), I'd like aspell-pt to be installed as a dependency of aspell, instead of aspell-en.
Sorry, this is completely impossible. Virtuals are global and completely unaware of your locale. If you want something feasible, then see Bug 48072, dictionaries could be installed w/ aspell based on LINGUAS.