KOrganizer provides a wide range of customizability. Like all KDE applications it is translated to a lot of languages, currently more than 50.
You need a Chinese, a German or a French Organizer? No problem, KOrganizer speaks your language.
But it doesn't stop at the language. KOrganizer also supports localisation of date formats or country-specific holidays. You prefer to start your week on Sunday rather than Monday? No problem, just switch it.