It's a common misconception among our translation clients that -ise is English and -ize American. Not true: both are UK English. Dr. Johnson clouded the issue with his dictionary because he had the idea that all words ending in -ize were derived from French and so should be spelt the French way, with -ise. In the end, he was as bad as Webster. And had weapons-grade halitosis to boot.
Anyway, our clients often ask for translation into UK or US English, and get all hissy if we put an -ize in what they think is the wrong place.
Tiresome bugger, Johnson.