在手册中，请注意该类是intl扩展的一部分.请参阅安装说明中的国际说明，并注意需要明确安装使用-enable-intl 和/或可能需要ICU库，具体取决于系统.检查您的PHP安装是否已安装intl.

In the manual, note that the class is part of the intl extension. See the Installation Instructions for intl and note that it needs to be explicitly installed using --enable-intl and/or may require the ICU library, depending on the system. Check your PHP installation whether intl is installed or not.