https://bugs.winehq.org/show_bug.cgi?id=43630
--- Comment #7 from Fabian Maurer dark.shadow4@web.de --- Thanks for investigation. Also tested a bit today, and that's what I found:
The program uses EM_STREAMIN to read in the file. When using the German rtf, the program calls EM_STREAMIN twice - first with rtf, but then it reads it as text (wParam is SF_TEXT). When adding a hack to skip the first iteration, it indeed does display fine.
Problem is AFAIK due to a faulty rtf reader, still no clue why the program calls EM_STREAMIN again though. As said, it first does read the rtf properly, then throws everything away and reads it as plain text. Maybe some error state inside the rich edit control? Either way, I'm not entirely sure what causes the issue, but removing all occurrences of '\r' in the rtf file seems to solve the issue.