Bananen är övermogen.

Because bananen is the definite singular form of banana.

• en banana = a banana
• bananen = the banana

In Swedish, definiteness is often shown by adding an ending to the noun, instead of using a separate word like the.

Swedish usually puts the onto the end of the noun as a suffix.

So instead of:

• English: the banana

you get:

• Swedish: bananen

This -en ending marks the noun as definite. Since that ending already means the, you do not need a separate word.

Because banana is an en-word in Swedish, also called common gender.

Its forms are:

• en banana = a banana
• bananan would be wrong
• bananen = the banana

For most en-words, the definite singular ending is -en. Since banana is an en-word, its definite form becomes bananen.

Är means is / are / am.

It is the present tense of att vara = to be.

A helpful thing for English speakers is that Swedish verbs do not change depending on the subject:

• jag är = I am
• du är = you are
• bananen är = the banana is
• vi är = we are

So är stays the same.

Because the adjective has to agree with the noun, and here the noun is:

• singular
• common gender
• used with a predicate adjective after är

For a singular en-word, the basic form is used:

• en övermogen banan = an overripe banana
• bananen är övermogen = the banana is overripe

Compare:

• ett äpple är övermoget = an apple is overripe
• bananerna är övermogna = the bananas are overripe

So:

• common singular: övermogen
• neuter singular: övermoget
• plural: övermogna

Because after är, Swedish uses a predicate adjective, and predicate adjectives do not take the definite form in the same way that attributive adjectives do.

Compare:

• den övermogna bananen = the overripe banana
  Here the adjective comes before the noun, so it takes the definite/plural-style form övermogna.

But:

• bananen är övermogen = the banana is overripe
  Here the adjective comes after är, so it agrees by gender/number, not by definiteness.

That difference is very common in Swedish.

It is made up of:

• över- = over-, too much
• mogen = ripe

So övermogen literally means over-ripe, or more naturally in English, overripe.

• mogen = ripe
• övermogen = overripe

So:

• Bananen är mogen = The banana is ripe
• Bananen är övermogen = The banana is overripe

Övermogen suggests it has gone past the ideal stage.

A simple learner-friendly pronunciation guide would be:

bah-NAH-nen air OH-ver-moo-gen

A few useful notes:

• ä in är sounds somewhat like the e in bed, but longer depending on speech.
• g in mogen is pronounced as a hard g here.
• The stress is typically on:
  • -na- in bananen
  • ö- in övermogen

If you want a more Swedish-like feel, try to keep the sentence flowing smoothly:

ba-NA-nen är Ö-ver-mo-gen

No, this is the normal basic Swedish word order:

subject + verb + adjective

• Bananen = subject
• är = verb
• övermogen = adjective

So it works just like English:

• The banana is overripe

This is the most natural order in a normal statement.

Yes, but it means something slightly different.

• Bananen är övermogen = The banana is overripe
  This describes its current state.

• Bananen blir övermogen = The banana is becoming overripe / gets overripe
  This focuses more on a change or process.

So är describes a state, while blir often describes becoming.

That would be:

Bananerna är övermogna.

Breakdown:

• bananer = bananas
• bananerna = the bananas
• övermogna = plural form of the adjective

So the singular/plural contrast is:

• Bananen är övermogen.
• Bananerna är övermogna.

Yes. That means an overripe banana.

This is the same adjective used before the noun:

• en övermogen banan = an overripe banana

Compare with your sentence:

• Bananen är övermogen = The banana is overripe

So Swedish can express the same idea in two common ways:

• adjective before the noun: en övermogen banan
• adjective after är: bananen är övermogen