See: http://blogs.testbit.eu/timj/2005/06/20/02062005/ (page moved)
The intltool vs. scheme saga continues. Basically, Kevin Cozens (the gimp script-fu / tiny-fu maintainer) is willing to use proper markup for scheme strings via a (_ ) function, however applying such a change is post tiny-fu-1.0 stuff, so won’t happen too soon.