In my quest to fiddle around with a ton of development environments (because so far I've hated them all), I decided to try out gEdit to write some Scala. My initial impression is that it's very similar to jEdit (for the purpose of writing Scala), but the syntax highlighting from the Scala Bazaar doesn't work (boo). So.. I decided to write up a simple lang file for gEdit. Verdict: jEdit is now removed from my system.
Copy scala.lang to /usr/share/gtksourceview-2.0/language-specs and restart gEdit to install this thing.
The original file from scala-tool-support will work if you create the scala mime type in /usr/share/mime. You can view this sample file or just drop it in there. Then drop scala.lang into ~/.gnome2/gtksourceview-1.0/language-specs and you are good to go.
I submitted a patch for this so you should find the language file in scala-tool-support.