Localisation: -ise or -ize?

The -ise versus -ize debate is one of the most visible spelling differences between British and American English. Words like localise/localize, organise/organize, recognise/recognize, and optimise/optimize follow this pattern across hundreds of common terms. Both spellings are linguistically valid — the -ize ending is actually older in English — but today they function as regional markers that signal to readers whether content comes from British or American conventions.

The differences extend well beyond verb endings. British English uses -our where American English uses -or: colour/color, behaviour/behavior, honour/honor. British English uses -re endings where American uses -er: centre/center, theatre/theater, metre/meter. British English tends towards -ence where American English uses -se: licence/license, defence/defense. These patterns affect dozens of words that appear throughout software interfaces — button labels, error messages, help text.

For software localisation, this matters in practice. An application targeting UK audiences that consistently uses American spellings risks appearing careless to British users, even if the content is otherwise accurate. The reverse applies equally — British spellings in software aimed at the US market may feel unfamiliar.

The most robust approach is to treat en-GB and en-US as distinct locales rather than assuming one English serves all markets. Language Monster supports both as separate target languages, letting your team maintain dedicated translation files for each English variant. You can start from a shared base and branch only the keys that differ, keeping maintenance overhead low while ensuring each audience receives the spelling conventions they expect.