How to change the spell-check to British -ize in Mac?
It is possible to change the spelling dictionary to either British (-ise) or American (-ize) as shown in the solution to this post.
However, I would like to use British spelling with -ize variant (recalled as en_GB-ize in some dictionaries). Is there a way to set this language in Mac?
Try setting your spellcheck language to Canadian English.
An alternative would be to see if you can find a 3rd party dictionary that does what you want from sources like this.