Name of day/days for duration
This is a i18n option! i18n options can not be set directly on a per-instance basis, you must include the "override" directive, and properly camel case the new name - (i.e. overrideDurationDays). For more information, please take a look at the Localizing Datebox section.
Pluralization of Day/Days. (1 Day, 2 Days). Very simplistic, for instance, there is no support for 0 Days. Nor any other cases in different locales that don’t follow the english method of pluralization.