This is a known limitation of the engine. The setting ignorePlurals , which is intended to treat singular, plurals, and other forms of declensions as matching terms, doesn't work in the Danish language (i.e the word børn "children" won't be seen as barn, "child").
You can work around this by adding them to the dictionary to address this issue: go to Algolia Dashboard > Search > Dictionaries > Plurals & Other Declensions. Read more about this here.