"De er ikke officielle."
Translation:They are not official.
Does the spelling of 'officiel' change depending on whether the subject being spoken of is singular or plural?
Yes, if it's common gender there is no declension: 'En officiel mand' (an official husband). However, if it's neuter gender then it declines with a -t: 'Et officielt kone' (an official wife). When there is a plural, though, you decline it -e, in this case the l on 'officiel' doubles up: 'Officielle aviser' (official newspapers). You also use this -e declension when the adjective in between a definite article and the noun: 'Den officielle avis' (The official newspaper). And when the adjective follows a possessive pronoun: 'din officielle avis' (your official newspaper). These rules apply to all regular adjectives. You can find a table of the declensions and more information regarding irregular adjectives in the Tips Notes of this skill.