For many of us, dates and times are absolutely essential in our daily lives. We make appointments, set deadlines, celebrate birthdays and anniversaries, and generally mark time using clocks and calendars.
What makes dates and times interesting from a programmer’s perspective is that while there is a standard time (the Coordinated Universal Time or UTC), there are multiple local time zones in use all over the world. A single instance in UTC has many local equivalents, and offsets between time zones and universal time are wild and wonderful.
Not only are time zones a little tricky, but there are also multiple local representations for an instance in local time. A representation in this context means the way it is printed in a daily newspaper, in the calendar, and indeed, on the screen of a computer or a mobile device. In the realm of internationalization (I18N) they are known as date and time formats.
The conventions for showing local time are well established, and the differences between them are significant enough to cause a lot of confusion if care is not taken. While it would be the most logical thing to do (thank you Mr. Spock), it is hardly practical to expect all the world’s population to adopt a single standard date and time format such as the ISO 8601 international standard notation in their daily lives. The national and linguistic conventions are very well established locally.
Just recently, Nokia launched new Windows Phone devices in their Lumia series. The company wanted to build anticipation before the announcement with short teaser videos which all marked the date of the launch: 05.09.2012. If you saw this date advertised early in the year, you might think it could mean either September 5th or May 9th this year. But which is it?