intfiction.org

Are there any TADS 3 interpreters for GNOME or based on GTK2?

Nope. But QTads supports GNOME (by looking and behaving like a Gtk application) if you have a recent enough Qt library installed (4.5 and newer).

Gargoyle uses Gtk2 under Linux, but it does not support any of the multimedia features.

I had the impression Gargoyle uses SDL for display.

Just for audio. Fonts and images are composited to an internal bitmap buffer. Display is handled by drawing the final bitmap to the screen.

That part could be done with SDL but it only amounts to a few lines of code per OS target.

Unfortunately, Gargoyle doesn't seem to receive text input in the same manner other programs to, I couldn't type in anything using my IME, also it currently doesn't appear to support uft-8, so my foreign-language game files appear as a lot of ????. I'll stick with qtads.