Every country has a different way of displaying numbers and currencies, even if you will be displaying the same number.

localeconv()
The localconv() function will give you all necessary information about the current locale. 

<?php
$c = localeconv();
var_dump($c);
?>
number_format()
The number_format() function along with localeconv() will allow you to get locale specific information. 

<?php
$linfo = localeconv();

function locale_num ($n) 
{
    global $linfo;

    return number_format($n, 
                         $linfo['decimal_point'], 
                         $linfo['thousands_sep']);
}

print locale_num(100);
print locale_num(200203002);
print locale_num(139939.23321);
?>