When to Use ‘the Honourable’ British Spelling
The Honourable is used in direct address with e.g., a son of a viscount or baron; wife of the son of a viscount or baron; a younger son of an earl or viscount; wife of a younger son of an earl; daughter of an earl, viscount, or baron.
The Right Honourable is a courtesy title used with certain current and former British Commonwealth officials such as members of the Queen’s Privy Council. It is typically abbreviated the Right Hon.
—–#1) The Honourable and the Right Honourable (both with a U like colour, flavour and armour) are British courtesy titles. The are not merely words to be translated – they are parts of a person’s name. Because it is considerate to write a person’s name exactly as he or she writes their name, use the British spelling with Commonwealth citizens and officials of former Commonwealth countries using British spellings.
—–#2) It is correct for an American to use the American spelling –– the Honorable –– with U.S. officials and officials of non-English speaking countries that use the Honorable as a courtesy title.
— Robert Hickey