Poll app language setting

I want to change the language for texts presented to anonymous users from English to Danish.
The directory l10n seems to have lots og language files including Danish, but how to I make the app use the da.js / da.json files ?

I would assume, that you need to set your preferred language in your personal Nextcloud settings.

That does not change the texts, that Poll displays to anonymous guests.
And actually alle users and det site language is set to da_DK
But poll still displays English texts despite that it do have Danish texts defined.

So my question is: How do I force Danish texts in Poll?