Wordpress UTF-8 problem after PHP upgrade (from 5.6 to 7.3)

["Christoph K." <christoph@kobenetz.de>]

Hello,

I've just upgraded from PHP 5.6 to PHP 7.3 (and reverted back for now).

With PHP 7.3 there is a problem in Wordpress displaying german Umlaute
and other UTF-8 related characters.

I guess it's just some locale-related setting somewhere,
any suggestions?

Thanks,
Christoph


Software version information:
Debian 10/Buster on amd64
MYSQL server 5.5
Apache 2.4.38
Wordpress 5.0 (that ships with Buster)

PHP / Wordpress compatibility chart
https://make.wordpress.org/core/handbook/references/php-compatibility-and-wordpress-versions/