I believe you have to get it from the Windows Registry.
powershellCmd = "powershell -command \!"(Get-ItemProperty -Path 'HKLM:\\SYSTEM\\CurrentControlSet\\Control\\TimeZoneInformation' -Name 'TimeZoneKeyName').TimeZoneKeyName\!"";
timezone = RunProgram(
executable("cmd.exe"),
options({"/C", powershellCmd}),
readFunction("Text")
);
Show(timezone);
Jim