Use date_i18n() from wp-includes/functions.php.

/**
 * Retrieve the date in localized format, based on timestamp.
 *
 * If the locale specifies the locale month and weekday, then the locale will
 * take over the format for the date. If it isn\'t, then the date format string
 * will be used instead.
 *
 * @since 0.71
 *
 * @param string $dateformatstring Format to display the date.
 * @param int $unixtimestamp Optional. Unix timestamp.
 * @param bool $gmt Optional, default is false. Whether to convert to GMT for time.
 * @return string The date, translated if locale specifies it.
 */
function date_i18n( $dateformatstring, $unixtimestamp = false, $gmt = false )