user defined message texts - cyrillic does not work

Dear Community, we are running Simotion D4x5-2 controllers in electrical equipment for power plants. We developed a specific Web-HMI in javascript plus AngularJS for the WebServer of the Simotion controller. Unfortunately for a project in Bulgaria we do have an issue with correct handling of cyrillic fonts in the messageHandling within Simotion.

Apparently the Web-HMI perfectly supports these cyrillic fonts, but the user defined message texts being located in these DAT-files on the CFcard under

\USER\SIMOTION\USER_DIR\UPP\UNITDS\flmsghdlinit

does not work at all. We double-checked that the DAT-files are generated correctly from UTF-8 encoded XML-origins.

For your experts review please see screenshot of WebHMI.

Your support is highly appreciated.