special characters corrupted when saving in WP admin panel

HELLO WP community,

I’ve encountered a very weird problem, and having gone through lots of tips and suggestions online, none of them have worked so far.

Problem: I was trying to save some Chinese characters as part of my menu navigation label in WP admin panel (under Appearance -> Menu), e.g. Say I wanna save “首页” into the label, but it turns out as “é|?é?μ”

I’ve tried setting charset and collation in config.php to utf8 and utf8_general_ci.
I’ve also checked all the database tables’ collations, it’s all utf8_general_ci.

the problem seems happening at the saving time only because I directly find that navigation label and edit inside the database through phpmyadmin, and it display the chineses character flawlessly in WP admin panel menu page, which means the WP can successfully read the chineses character from database without any problems. HOWEVER, when I save it again, it’s gets corrupted, so the problem must be at the stage where WP writes data into the database.

Any suggestions would be appreciated. THANK YOU.