"A dirty dog in a dirty house"
Translation:En skitten hund i et skittent hus
Adjectives are inflected based on the gender of the word they modify. Hund is masculine/feminine, so you use skitten; hus is neuter, so you use skittent.
It does take a while to get used to; I still haven't mastered it either. You'd think that the plural would be "skittene", but it's actually "skitne" because some series of syllables in inflected (especially plural) words tend to collapse down a bit. Keep practicing, it gets easier with time!