Most literal translation:
* Gall Duw farnu. (This translates directly to "God can judge.")
More poetic or emphatic translations:
* Duw yw'r barnwr. (This means "God is the judge" and emphasizes God's authority.)
* Mae gan Dduw y pŵer i farnu. (This means "God has the power to judge" and highlights God's ability.)
Informal translation:
* Gall Duw wneud barn. (This means "God can make judgment" and is more conversational.)
The best translation will depend on the context of your sentence.