Why can't I change spelling language from English to Danish?

No matter how many times I try English is still the language. Until now it has been possible.

Tools>Options>LanguageSettings>Languages>User Interface: Danish. If Danish is not availlable, get a Danish language package for your LO version.

Tools>Options>LanguageSettings>Languages>Default language for documents (Western): Danish
This will mark every word and every sentence you write as Danish. If there is a check mark in front of “Danish”, you have a Danish spell check dictionary installed, if not: Stavekontrolden - Danish Spellchecker » Extensions and install it via Tools>Extensions…

Apparently, what you try is wrong, but until you ask a good question, hardly anyone will help you.

gabix: Perhaps you could tell me what I do wrong and what a good question is?

It is already set like that and it has worked earlier

Now it is suddenly set to Danish, but now I cannot change it to English

What is “it”? User interface language? Text language of new document or existing document? Parts of documents may be tagged as English, other parts of the same document may be Danish.