PHP probably uses the system default locale. Use the following to make sure you use a specific locale:
setlocale(LC_ALL, 'nl_NL'); // for Dutch
see: http://www.php.net/manual/en/function.setlocale.php
Locale determines how date, currencies and numeric values are formatted. You can change the locale for specific PHP functions only (such as currency formatting).
Setting locale for currency only:
setlocale(LC_MONETARY, 'en_EN'); // for English
Setting locale for numeric formatting only:
setlocale(LC_NUMERIC, 'en_EN'); // for English
See above link for more detailed information on that topic.