The Japanese version intentionally does not allow the shutter sound to be turned off by any legal means. The reason for this is that it that there is a perception that photos being taken without the knowledge of the person being photographed is a real problem in Japan, especially “upskirt” photos. However, there are two tricks which can overcome this issue
If you jailbreak the phone, you can use a program like iPhoneBrowser to browse the file system of the iPhone and replace the file photoShutter.caf in /System/Library/Audio/UISounds with a different file. However, not every iPhone can be jailbroken or not everybody would like to jailbreak their iPhone
Use third-party Camera App
You can still take a photo without shutter sound by using third-party camera APPs like Varlens and Microsoft Pix. Follow the lead and you can start taking silent photo.
iPhone Live Photo
iPhone LivePhoto will capture a few second of sounds while snapping the photo, so it is impossible for LivePhoto function to turn on the shutter sound continuously for a short period.