title: How to get 12 hour format time string when system is set to use 24 hour format
body: <p>I want to get a time string like "10:00 PM", and I use the NSDateFormatterShortStyle to achieve this.
  However when the system is set to use 24-hour format, what I got is "22:00".</p>
  
  <p>Besides, I want to get a localized time string. For example, in Chinese, I want to get "下午10:00" instead of "10:00 PM". So I have to use the [NSLocale currentLocale], and can't use the en_US_POSIX locale.</p>
  
  <p>Please help me to get a localized 12-hour format time string.</p>
  
  <p>I need not only the hour part, and also the am/pm part. Besides, am/pm part may locate before the hour/minute part or after the hour/minute part depending on locale. Just like the system display time.
  When system is set to use 12-hour format, it's just simple. But when the system is using 24-hour format, I just can't get the localized 12-hour format time string.</p>