Read about the intl extension
intl extension manual page.
It definitely has uses as it allows you to collate and format certain data (dates, currency, numbers, etc.) according to a locale setting.
Example (from PHP.net):
$fmt = numfmt_create( 'de_DE', NumberFormatter::CURRENCY );
echo numfmt_format_currency($fmt, 1234567.891234567890000, "EUR")."\n";
echo numfmt_format_currency($fmt, 1234567.891234567890000, "RUR")."\n";
$fmt = numfmt_create( 'ru_RU', NumberFormatter::CURRENCY );
echo numfmt_format_currency($fmt, 1234567.891234567890000, "EUR")."\n";
echo numfmt_format_currency($fmt, 1234567.891234567890000, "RUR")."\n";
Output:
1.234.567,89 €
1.234.567,89 RUR
1 234 567,89€
1 234 567,89р.*Edit: Forgot to answer second question -
As far as the code accelerator is concerned, not that I can see. However, they have modified the garbage collector to track cyclic references. While poking around, I have also noticed numeros functions designated as 'now works regardless of system' though I can't recall any specific examples.