Sharia in Washington State?

Lately there's been a lot of silly fearmongering about US courts applying Sharia law. Sometimes US courts do have to get into foreign law, though, and the results can be odd.

In re Marriage of Akon, 160 Wn.App. 48, 248 P.3d 94 (2011) was a child custody/paternity dispute between some Sudanese refugees that turned on whether the mother's first marriage in the Sudan was valid. Apparently her husband had agreed to pay her father fifty cows for her on a time payment arrangement, but had only paid thirty five when the civil war reached the village and they all fled, with Mom eventually ending up in Spokane with another man. When that relationship fell apart, a dispute developed as to which she was married to. Thus, the Washington courts were left with the unenviable task of figuring out the effect of a debt of fifteen cows on the validity of a marriage under Sudanese law.

Now, judges would always prefer to apply the law they're familiar with. I'm sure the judge in this case was buying Excedrin at Costco by the time it was done. Judges have to apply the law to real life people with real life issues, and it's not always simple. What would have happened if the judge was forbidden from considering foreign law in the Akon case?