Created attachment 104354 [details]
Example files and screenshots showing the file in Writer and Notepad++ for comparison

Follow these steps:

1. Open "opened_correctly.d" in LibreOffice writer. Writer will use the font "Liberation Mono" and it will open the file correctly. The same goes for dozens of other .d text files I tried.

2. Now open "opened_incorrectly" in LibreOffice writer. Writer will use "Courier" as font and in the end there are some parts missing. In LibreOffice it will say:

...
	AI_Output (self, other,"Grd_264_Gardist_GARDEAUFNAHME_Info_07_02"); //Geh doch mal zum Alten Lager und sprich mit Thorus darckgebracht hab, sollte ich mal mit Thorus reden. Vielleicht nimmt er mich in die Reihen der Gardisten auf."); 
...

3. Now for comparison open "opened_incorrectly" in Notepad.exe. Here it will open the file correctly:

...
	AI_Output (self, other,"Grd_264_Gardist_GARDEAUFNAHME_Info_07_02"); //Geh doch mal zum Alten Lager und sprich mit Thorus darüber!
	
	Log_CreateTopic (GE_BecomeGuard,LOG_NOTE);
	B_LogEntry (GE_BecomeGuard,"Wenn ich die Eier zurückgebracht hab, sollte ich mal mit Thorus reden. Vielleicht nimmt er mich in die Reihen der Gardisten auf.");
...



As you can see LibreOffice will skip the part after the ü character and then continue after the next ü character. However "opened_correctly" also contains ü characters.