Notify problem in "Action Objects"

[pincode]

There is no possibility to use Russian letters in the body of the notification.
When trying to send a message in the /var/log/mail.err log, an error occurs:

open body: Invalid argument at /usr/share/perl5/MIME/Entity.pm line 1878.

My users would like to receive alerts in their native language. Tell me, how can this be fixed?
Proxmox mail GW version: 5.2-1