Hello Natalia,
The email notification is sent by script sap_core_notificationByEmail of job "Send email notification" in SAP provisioning framework in this case. In the script, this is done by uSendSMTPMessage. This u function has one parameter ContentType, which can be used to specify valid MIME content type. eg: you may try to specify it as "text/html; charset=ISO-8859-5", and test again.
BR, Keith