Hello,
I too have a Norwegian who has a spot on his tongue, and also on the roof of his mouth. When he was a baby, his veterinarian inspected both areas and told me they were harmless, similar to birthmarks. Some breeds are more likely to have this characteristic than others.
If you've just noticed the spot, though, monitor it for a few weeks and be sure that it remains the same size, shape, and color. If there are changes, you may want to bring your cat to the vet for an inspection.
Blessings,
oceandeep12