- Type something in any application you want that supports spell-check (Mail, TextEdit, etc.).
- Control click on any word at all.
- From the pop-up menu you want Spelling > Spelling...
- Choose your preferred language from the pop-up.
The test I used was to mistype aluminum/aluminium as "alumiium". If you're in British English version you are offered "aluminium" and if in US English "aluminum"

