Here are a few things that might help:
A brief how-to on installing extensions in OO.org 3.x:http://extensions.services.openoffice.org/resources/user/howto_install
On my machine, the English language extension was in:
The English dictionary I found there was the file:
I used the Extension manager to add the dictionary. After that I had to restart OO, but then spell checking worked.
I still haven't found extensions for the varieties of English (UK, Australia, Canada, US, etc.) but will add another post when/if I find something.
Addendum: There are extensions for Canadian and Australian English at http://extensions.services.openoffice.org
, along with a few other languages.
No luck so far with finding a UK English extension.
Addendum II: toothandnail
, and all other UK English users (the Queen's, dontcha know): all that needs to be done is to set your language preferences (under Tools -> Options -> Language Settings -> Languages) to look like this
The "dict-en.oxt" will need to be added to your extensions beforehand. It looks like with this extension UK and US English are rolled together, and spell checking is done based on your language settings. After I changed my settings to UK, "honour" wasn't flagged but "honor" was. I tried a few other words (aluminium, colour, etc.) and they were all right as well.