Learn Swedish: Försäljaren säger ju att äpplena är mogna. - The vendor says the apples are ripe, you know.

The base adjective is mogen (ripe). Because it ends in an unstressed -en, it drops the e before adding the plural ending -a. So, it becomes mogna to match the plural äpplena. This is a common pattern for adjectives ending in -el, -er, and -en.

What is the word ju doing in this sentence?

ju is a common little word (a particle) used when you expect the listener to agree with you or when stating a known fact. Here, it translates well to "you know." It gives the sentence a conversational tone, as if saying "Well, the vendor said so, right?"

How do we build the word äpplena (the apples)?

The root word is ett äpple (an apple). For ett words that end in a vowel, the plural is formed by adding -n, making it äpplen (apples). To make that plural definite (the apples), you add -a to the end, resulting in äpplena.

The word for vendor is försäljare. Why is the definite form försäljaren instead of just adding an -n?