Is there a Norse god/goddess of law or justice? Or is law/justice a too western of concept to have back then?
Tyr was a norse God of law and war. Evidence suggests that he was once head of the pantheon, but was supplanted by Odin and Thor. He was wise and brave, the only of the gods courageous enough to offer his hand as collateral when they wanted to bind Fenris.
Forseti, the son of Balder, is mentioned by Snorri as a good mediator and judge. His name also means "the presiding one", so he has been linked with law and justice by scholars.