while England was doing this the germanic people actually had a decent law system
- All the way until William the Conqueror, England was downright Germanic.
- Ordeal of combat was specifically Germanic custom. Only later was it introduced in other places (under Germanic influence).
Jury was introduced in England in 13th century, under papal influence. That's about the timely equivalent of Planeshift's setting. But historical accuracy has very little to say here.
1) If we want to be historically correct, the punishment wouldn't be paying tria, but cutting off hands or tongues. Would players appreciate that?
2) It's not hard to find jury trials in TV and rich popular references. Will those then be attractive additions for a medieval setting? Will they let players cut free from the modern culture?
The trial by combat was, unless I'm mistaken, reserved for Nobility
It wasn't reserved for anyone, although it would be ordeal of choice for the rich and nobility. One reason for this was that you could simply hire combatant specially trained for such ordeals to fight instead of you. Don't remember the English name for those combatants though.
As to ordeal of fire and water, I would Yliakumize it. Cast a spell that causes minor radiation, akin to that of the Azure Sun. If the radiation harms the accused, they're guilty. If i doesn't, apparently they didn't do anything. Of course, it doesn't have to be always right ;)