I'm running FreeBSD 12.1-RELEASE in VirtualBox on Windows 10.

  $ uname -a
  FreeBSD vm-freebsd 12.1-RELEASE FreeBSD 12.1-RELEASE r354233 GENERIC  i386

The following reduced program results in a segmentation fault.

  $ cat test1.c
  #include <locale.h>
  #include <stdio.h>

  int main(int argc, char** argv) {
    int i;

    if (argc != 2) return 2;
    printf("start\n");
    fflush(stdout);
    for (i = 0; i < 100000; i++) {
      setlocale(LC_COLLATE, argv[1]);
      setlocale(LC_COLLATE, "C");
    }
    printf("done\n");
    fflush(stdout);
    return 0;
  }
  $ gcc -o test1 test1.c
  $ ./test1 en_US.UTF-8
  start
  Segmentation fault
  $ ./test1 ja_JP.UTF-8
  start
  Segmentation fault
  $ ./test1 ja_JP.eucJP
  start
  Segmentation fault

The number of successful invocation of `setlocale' until the
segmentation fault is always the same for the same locale, but it is
different for different locales.  The segmentation fault is only
caused when the category LC_COLLATE is changed (through LC_COLLTE or
LC_ALL).  There are no problems with the other categories.

I suspect the implementation of `__collate_load_tables_l' in
`lib/libc/locale/collate.c'.  I'm not sure but maybe there is a memory
leak caused by missing `munmap'?

https://github.com/freebsd/freebsd/blob/b6fca3ee8065a5cfd3a36abfd7a2663eb5bfee7d/lib/libc/locale/collate.c#L184