The Swedish language : 5th part, grammar : adjectives

The Swedish adjectives agree with gender and number (as in French) with the following word. The ending gets an -t at singular and neuter, and an -a at plural.
Undefined :

• En vacker sjö : A beautiful lake
• Ett vackert hav : A beautiful sea
• Vackra sjöar : Beautiful lakes
• Vackra hav : Beautiful seas

Defined :

• Den vackra sjön : The beautiful lake
• Det vackra havet : The beautiful sea
• De vackra sjöarna : The beautiful lakes
• De vackra haven : The beautiful seas

We can see that an article (the pronoun de) is used at plural.