Adicione o seguinte conteúdo no arquivo ~/.kde/share/config/kdeglobals
[General]
fixed=Monospace,10,-1,10,50,0,0,0,0,0
font=DejaVu Sans Condensed,9,-1,9,0,0,0,0,0,0
menuFont=DejaVu Sans Condensed,9,-1,9,0,0,0,0,0,0
taskbarFont=DejaVu Sans Condensed,9,-1,9,0,0,0,0,0,0
toolBarFont=DejaVu Sans Condensed,9,-1,9,0,0,0,0,0,0
--
Guilherme França
Até mais e boa sorte.