No, the Gregorian calendar does not need to be reformed and worldwide calendars do not to be standardized, because the world has been managing with multiple calendars just fine. Throughout modern history, people have managed on multiple languages, multiple time zones, multiple units of measurement. There is no reason to change the calendar now.
No, the Gregorian calculator does not need to be reformed, and worldwide calendars do not need to be standardized, because the Gregorian calendar has been working for the world just fine since its inception. There are not major problems with it, and the minor ones that technology has produced, technology has also been able to solve. There is no reason to break from tradition.