Steps to reproduce. Open windows file explorer Right click on empty space and choose New -> Microsoft Word Document. Specify some file name, with .docx extension. Now open this empty file using libreoffice Writer. Change to a different input language ( I tries sanskrit, tamil). Enter some characters in this other language. Save the files as .docx itself. Now, re-open the file using libreoffice Writer. Entered characters are showing as ? plain question marks.
*** This bug has been marked as a duplicate of bug 143093 ***