In Europe
You can hold an NPPL SLMG (not technically a 'full' SSEA PPL) or a JAR PPL with a TMG rating (a full PPL). A Glider licence on its own is not sufficient to fly an SLMG or TMG.
My earlier post refers regarding what I believe is easiest system for Gllider Pilots requiring to fly any glider with an engine - the FAA system in the US.
Arc