Regional differences mean that game released for same platform may look partially different in different countries and/or regions. This can refer to censored elements such as violence, adult scenes, or certain references, or it can mean the game simply has changes in its presentation, story, gameplay, but not enough to warrant a new game entry. Preferably, the differences should be mentioned either in game description or in the trivia section if known. Note that this does not apply to port differences where game is changed when ported to a different platform. This attribute only applies to game being partially different when played in different country, aside from change of text and voice-acting language.
This genre does not apply for localized differences. Localization is almost sure to change dialogues, inside jokes and character names to make more sense to the country and language in question. For example "Ace Attorney / Gyakuten Saiban" games feature Phoenix Wright (US) and Ryuichi Naruhodo (JP) names for the main protagonist. In English "Wright" is often used to imply that he is "right" in a comical sense during dialogues. In Japanese version, "Naruhodo" as a read-word means "of course" which adds more humor to Japanese dialogues. Such localizations are assumed and there's a team of developers that does localization to different languages. Direct translation isn't always possible as different languages simply don't have all the same words or a way to exactly depict what is being said. In a same way, joke in one language literally translated to another may not be funny at all, especially if it's a word play. So, regional differences does not entail localization differences which are assumed for every officially locally translated game.