Python is much better than Java for rapid prototyping, and is much easier to learn. It also happens to have bindings for QT and GTK and be work well with C and C++ bindings and is available (and commonly used) in Maemo. The lack of java is actually a selling point for me. It's been so overhyped for the last ten years that it is used for all kinds of problems that it's just not that suited for.

Anyway, Rapier is python/C++. I suspect it's the path of least resistance since it should be easier to modify than reinvent a Sword wheel. (hehe a sword wheel)

Edit: took too long to reply. I noticed BPBible also uses Sword, and Python. I didn't look too closely, but that may be another option. Did you play with Rapier itself?