Hello MHA,
Unfortunately I have been unable to find a Danish translation of XenForo.
Have you considered translating it yourself?
Although this might seem like a daunting task, the process is relatively straight forward. It is obviously a lengthy process (there are around 4500 phrases to translate) but if your preferred forum software is XenForo then it might be worth the extra work.
You could then even release it in the Resource Manager for other Danish customers to enjoy.
Also, sorry for the delayed response... responses are usually quicker...