为什么localeconv（）在Linux上的意大利语（it_IT）中为thousands_sep返回空字符串（“”）？

Question

为什么localeconv（）在Linux上的意大利语（it_IT）中为thousands_sep返回空字符串（“”）？它在Mac OS X上运行良好。

#include <stdio.h>
#include <locale.h>

int main () {
   struct lconv * lc;

   printf("locale %s\n", setlocale(LC_NUMERIC, "it_IT"));
   lc = localeconv();
   printf("Thousands Sep: %s\n",lc->thousands_sep);
   printf("Decimal Point = %s\n", lc->decimal_point);

   printf("locale %s\n", setlocale(LC_NUMERIC, "en_US"));
   lc = localeconv();
   printf("Thousands Sep: %s\n",lc->thousands_sep);
   printf("Decimal Point = %s\n", lc->decimal_point);

   return 0;
}

Mac OS X 10.9.1：

locale it_IT
Thousands Sep: . 
Decimal Point = ,
locale en_US
Thousands Sep: ,
Decimal Point = .

Ubuntu 12.10：

locale it_IT
Thousands Sep: 
Decimal Point = ,
locale en_US
Thousands Sep: ,
Decimal Point = .

CentOS 6.5：

locale it_IT
Thousands Sep: 
Decimal Point = ,
locale en_US
Thousands Sep: ,
Decimal Point = .