- printf: documentation ( source)
<?php
printf("%6.2f",5.678);
$a = new \NumberFormatter("it-IT", \NumberFormatter::DECIMAL);
echo $a->format(12345.12345) . "<br>"; // outputs 12.345,12
$a->setAttribute(\NumberFormatter::MIN_FRACTION_DIGITS, 0);
$a->setAttribute(\NumberFormatter::MAX_FRACTION_DIGITS, 100); // by default some locales got max 2 fraction digits, that is probably not what you want
echo $a->format(12345.12345) . "<br>"; // outputs 12.345,12345