I believe it is more a weakness of LibreOffice Draw not to be able to read splines and text from a dxf than it is LibreCAD's fault. I have tested it with files from other CAD tools and it is the same result.
Why do you want to open the drawings in LibreOffice? Do you want to edit them further there? If you just want to insert them in a LibreOffice document for publishing you could export to pdf in LibreCAD and insert or open that in LibreOffice. This works, tested it.
In LibreCAD, if you use Spline, Degree 3, (only that, and not Spline through points), you can 'Explode' them afterwards and will have a succession of small straight line segments instead.
I don't know what ULSG WIBU is and what file formats it can use. Ask your teacher. In LibreCAD you also can export to svg, which can be used for CAM (computer aided manufacturing, like cutting machines), this may be an option. Svg export shows splines (have tested), but not text.