Comment 9 for bug 1308986

attached is a modified version of the file dxf_input.py. This can be tested by copying it to the directory Inkscape\share\extensions\.
This fixes the original issue caused by blank spaces. These are replaced with '_'. The symbol can now be dragged and dropped.

It does not address the issue related to non-Ascii characters. I suspect this will have to be handled as a separate bug, probably in the Symbols dialog code, not in Python.