Actually, the command to launch the program set in the desktop file is "sudo wlassistant".
I don't know if that works on some distros, but it doesn't for debian based ones...
It would be better to make usage of "kdesu".
Also, adding a GenericName and Categories might be usefull for a clean and clear entry in the K menu.
Here is what wlassistant.desktop could be like :
[Desktop Entry]
Encoding=UTF-8
Name=Wireless Assistant
Comment=A wireless LAN connection manager
Comment[pl]=Program do obsługi sieci bezprzewodowych
Comment[es]=Aplicación para buscar redes inalámbricas
Comment[fr]=Application permettant de gérer vos connections Wi-Fi
GenericName=Wireless LAN Manager
GenericName[fr]=Gestionnaire de réseau sans fil
Categories=Qt;KDE;Network;
Exec=kdesu wlassistant
Icon=wlassistant
Type=Application
Logged In: YES
user_id=1243212
Added categories. sudo will remain the preferred command
until I find something better that would not require user
input every first time.