localetest.c

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

int main (void) {
	
	struct lconv locale_structure;
	struct lconv *locale_ptr = &locale_structure;
	
	char *a = "ä";
	char *b = "b";
	char *c = "c";

	setlocale(LC_ALL, "de_DE.UTF-8");
	locale_ptr=localeconv();
			
	printf("Currency symbol: %s\n", locale_ptr->currency_symbol);
	printf("%s\n", a);
	printf("%d\n", strcoll(a, b));
	printf("%d\n", strcoll(b, c));
}

Output on Ubuntu 10.4, gcc 4.4.3:
Currency symbol: €
ä
-1
-1

Output on OS X 10.6.4, gcc 4.2.1:
Currency symbol: Eu
ä
130
-1