Bu avokado çok olgun, onu bugün yemeliyiz.

In Turkish, çok means very or much, and it comes before the adjective it modifies.

So:

• çok = very
• olgun = ripe / mature

Therefore:

• çok olgun = very ripe

This is the normal Turkish order: intensifier + adjective.

Yes. Olgun can mean:

• ripe for fruit
• mature for people, ideas, behavior, etc.

In this sentence, because we are talking about an avocado, olgun clearly means ripe.

In Turkish, the present-tense to be is often not expressed in the 3rd person.

So:

• Bu avokado çok olgun literally looks like This avocado very ripe
• but it means This avocado is very ripe

This is completely normal Turkish. The verb to be is understood.

Bu means this.

So:

• Bu avokado = this avocado

Turkish does not use articles like the and a/an the way English does. Instead, words like bu and bir often do some of that work.

Here, bu makes the avocado specific and near the speaker: this avocado.

Because onu is the accusative form of o.

• o = he / she / it / that
• onu = him / her / it / that as a definite direct object

In onu bugün yemeliyiz, the avocado is the thing being eaten, so it is the direct object. Turkish marks a definite direct object with the accusative ending.

So:

• o = it
• onu = it, as the object of the verb

The -u is the accusative ending, and the n is a buffer consonant.

The pronoun base is o. When Turkish adds certain endings to pronouns or demonstratives, a linking n often appears:

• o → onu
• bu → bunu
• şu → şunu

So onu is not a completely separate word you just memorize in isolation; it is o plus object marking.

Yes, you often could.

Difference:

• onu = it
• bunu = this one / this

In this sentence, onu refers back to bu avokado as it. That is very natural.

But bunu bugün yemeliyiz would also be understandable and natural in many contexts, especially if you are still pointing to or focusing on this avocado specifically.

Very roughly:

• Bu avokado çok olgun, onu bugün yemeliyiz.
  = This avocado is very ripe; we should eat it today.

• Bu avokado çok olgun, bunu bugün yemeliyiz.
  = This avocado is very ripe; we should eat this one today.

Bugün means today.

In Turkish, time expressions are often placed before the verb, so:

• onu bugün yemeliyiz = we should eat it today

That word order is very natural. Turkish word order is somewhat flexible, but the verb commonly comes at the end.

Yemeliyiz means we should eat or we must eat, depending on context.

It breaks down like this:

• ye- = eat
• -meli / -malı = should / must
• -yiz = we are / we (1st person plural ending here)

So:

• ye-meli-yiz = we should eat

This form is called the necessitative. It expresses obligation, advice, or strong recommendation.

The y is a linking consonant.

Without it, Turkish would have awkward vowel contact between parts of the word. So when endings are added, a buffer sound like y may appear.

Here:

• ye-meli-iz would sound awkward
• so it becomes ye-meli-yiz

This kind of linking consonant is very common in Turkish.

Because Turkish is typically an SOV language: subject – object – verb.

Here the understood subject is we, the object is onu, and the verb is yemeliyiz.

So the order is:

• onu = it
• bugün = today
• yemeliyiz = we should eat

Literally: it today should-we-eat

That final-verb position is one of the most important patterns in Turkish sentence structure.

It can mean either, depending on tone and context.

Most often, -meli / -malı is taught as should, but in real life it can range from:

• mild advice: should
• sensible necessity: ought to
• stronger obligation: must

In this sentence, because the avocado is very ripe and may go bad, we should eat it today is the most natural English translation.

Because Turkish verbs usually show the subject in the ending.

In yemeliyiz, the ending already tells you the subject is we.

So Turkish often leaves pronouns out when they are already clear from the verb form.

You could add biz for emphasis:

• Biz onu bugün yemeliyiz. = We should eat it today.

But normally it is unnecessary.