This problem is a bug which I will fix in Trunk Notes 1.9.0 which will be submitted to Apple in the next few days.
The issue is that Trunk Notes tries to capitalise the first letter of each word in the page name. The routine works with standard ASCII characters (a, b, c, etc) but seems to be getting confused with the letters you mentioned.
I have to admit my ignorance of languages other than English! Can you capitalise the letters Å, Æ, Ø - or are they already capitals? Should they not be capitalised? Any advice on this would be greatly received!
As a workaround you should be able to turn off the capitalise wiki words setting in the Settings apps.
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