I'm an immigrant in Norway. I do not have children, but have heard the stories. I used to hear some of the same stories in the American system, which also tends to not release details to protect the children.
Norway has strict laws about children and children have rights. These laws aren't bent because one is from another culture and living here. For example, physical punishment is pretty common in the US, but it is outright illegal here. It is seen as child abuse. If you have a drug problem, you might get your children taken away until you get yourself straigtened out. Sometimes you have to have classes or observation, and sometimes your children are removed until you do so. And honestly, from what I've seen with other immigrants, so long as you are following Norwegian law with the child, there isn't a problem.
> Parents are under gag order.
This is to protect the children. You see, if everyone finds out about it, they might treat the child differently or it might cause hardship or embarrass the child. And equality between kids is really important, so this sort of thing is avoided.
> There is no appeal, proof, or any oversight.
This is simply untrue. It might take time to appeal, but one can. Proof is an odd thing, and if things aren't clear upfront, they will take steps to make sure that the child won't be in danger if it is true. One has avenues to get help, but one must work within the system and take the steps. I don't know how well they work with foreign social workers, but again, if it is illegal in the country, you might be out of luck. People usually are expected to follow the laws of the country they are in.
> Does not release any details about cases, to protect children... even if child is already dead.
Again, to protect children. In the case that the child dies, this is truly more to protect what might be innocent parties involved.
> Siblings are often split
This is not unique to Norway. Sometimes this is the only way to keep kids safe: Other times, this is done while the investigation is going on so that one child doesn't influence the others.
> Removed children must speak Norwegian, the mother tongue is suppressed.
First, the kids will learn once they get school age - or earlier, if they are in kindergarden. It would be expected if they live here for an extended time because otehrwise they will be singled out. This really is just an effect of living in a foreign country. Finding safe homes with speakers of every language would be very difficult, and again. Better to find safe homes. This isn't something deliberate to harm people.
> relatives of children have zero chance to get custody.
I don't know for sure, but I doubt this is true and more rumor than anything. It would depend on the situation. In some cases, there would be little chance because the relative wouldn't keep the child removed from the threat (parents), but other cases, it might be possible.
> anonymous surveys...
Proof, man. Otherwise this is just rumor.