If you have a powerful soldering iron and some solder with plenty of resin flux you can manage to terminate the cables. If you supply a good flux of solder the tinny bare copper tip of each wire will became tinned and slowly the heat will remove the varnish. I have re-done a few of these cables - a small block of resin was very useful to keep a "bath" of nice and clean bright solder while tinning the wires.
In some types of String the screening braid was also Litz type wire - it was much more difficult to solder as the insulation was much thicker.
In some types of String the screening braid was also Litz type wire - it was much more difficult to solder as the insulation was much thicker.