setlocale¶
setlocale() is a built-in PHP function that sets locale information, affecting string functions such as strtolower(), strtoupper(), strcmp(), strftime() and number formatting.
setlocale() changes a global state: once called, it affects all subsequent locale-sensitive operations in the same process. This makes it fragile in long-running applications or when multiple locales are needed simultaneously. The locale must be available on the host system, and availability varies across platforms.
For locale-aware string handling, the Intl extension provides a more robust and portable alternative, with classes such as Collator, NumberFormatter, and IntlDateFormatter.
setlocale() returns the new locale string on success, or false if the locale cannot be set.
<?php
// Set locale to French
setlocale(LC_ALL, 'fr_FR.UTF-8');
// Affects string and number functions globally
echo strtolower('É'); // may behave differently depending on locale
// Locale may not be available on all systems
if (setlocale(LC_ALL, 'fr_FR.UTF-8') === false) {
// locale not available on this host
}
// Prefer Intl for portable locale-aware operations
$formatter = new NumberFormatter('fr_FR', NumberFormatter::DECIMAL);
echo $formatter->format(1234567.89); // 1 234 567,89
?>
See also Implementing PHP localization: A complete guide.
Related : Internationalization Functions, strtolower(), strtoupper(), Locale
