Websites show garbled characters after Plesk update

Applicable to:

After Plesk micro-update websites show garbled characters;
Custom changes in my.ini file are overwritten after microupdate;
Previously default charset was changed from latin1 to some custom value, for example, to utf8, for client MySQL server in %plesk_dir%Databases\MySQL\my.ini;
After Plesk update charset was reset to default one.
The my.ini file in %plesk_dir%\Databases\MySQL\my.ini is always changing

Product issue:

#PPPM-10178 "Client my.ini 'character-set-server ' option is reset to default after MU"
Fixed in:
- Plesk Obsidian 12 March 2019 (fixed as PPP-41116)

Please consider updating your server:

If update is not possible for some reason you may try the following

temporary solution

As workaround, until fix available: