Configuring a Mac to use Oxford spelling I cannot figure out now to make my Mac (OS X 10.8) use Oxford spelling in its spell checker (note I am being absolutely precise in the use of that term)! For example, I want to be able to write "organize colours" without my Mac from underlining one of those words as a spelling error (whilst also recognising that the way I just spelled recognize was an error, as old habits die hard).

Neither the British nor American spelling options in the system preferences can do this, and it is just ever so slightly infuriating that a Mac that uses the Oxford Dictionary as its spelling dictionary will not use said dictionary's preferred spelling!
LibreOffice's British English dictionary has support for Oxford English. You can download the .dic and .aff files from https://github.com/ropensci/hunspell/tree/master/inst/dict and place the files in ~/Library/Spelling – either manually, or using the terminal:

wget https://raw.githubusercontent.com/ropensci/hunspell/master/inst/dict/en_GB.aff -O ~/Library/Spelling/en_GB.aff
wget https://raw.githubusercontent.com/ropensci/hunspell/master/inst/dict/en_GB.dic -O ~/Library/Spelling/en_GB.dic


Then log out and log in again, or restart your machine.

You should now be able to go to your keyboard preferences (Apple menu → System Preferences…), choose the Text tab and enable the new dictionary under Spelling. It should be called “British English (Library)”:



Here's a screenshot of a Safari text field spell checked with this dictionary:



P.S: If you choose to enable auto-detection of the language used for spell checking, it doesn't seem to use these “Library” dictionaries, so you might need to right click in text fields, open Spelling and grammar and explicitly set the language to British English (Library) to get it to work.