it seems this has been present for a long time and no one doing anything about it.

This issue is tracked here:
https://winscp.net/tracker/78

Meanwhile you can configure an external editor in WinSCP that supports UTF8:
https://winscp.net/eng/docs/ui_editor_preferences

i should have maybe posted this in the bug report...

it seems winscp opens files with its editor not in utf-8 format which causes problems when there are other than english characters in the file. i had to copy the file to local computer and open it in total commander and save as utf-8 format and then recopy it back to linux for the configuration to work. so i suggest that this is an essential feature in future versions.