When I lived in Norway and wanted to convert my then UK PPL into a Norwegian one after the "1 year on a foreign licence" privilages were up, I had to take an air law and R/T theory exam in Norwegian.
It took me a year before I could understand and speak enough to have a go.
At that time (1991) coverting any sort of Professional licence was simply not possible. The country was very protectionist regarding foreign workers taking jobs from the locals.
The advent of JAR is supposed to change all that, but Norway had so many differences and peculiarities that I would not be surprised if some sort of special requirements (favoring only locals) are still in place. Speaking the lingo always helps, at least you can argue your case.
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TwinComm