Return the number of characters in string $str having character encoding $encoding. A multi-byte character is counted as 1.

您的内部编码可能未设置为utf-8,因此也是如此

echo mb_strlen('òàùè','utf8');

或者在全球范围内设置utf8：

mb_internal_encoding('utf8');

然后呢

echo mb_strlen("òàùè");

会给4(demo)