Dava gelecek ay başlayacak.

Here, dava means a legal case, lawsuit, or trial, depending on context.

In everyday Turkish, dava is most commonly used for a court case. So this sentence is talking about some legal process that will begin next month.

A small note: dava can also mean cause or ideal in some contexts, but that is not the meaning here.

In this sentence, gelecek is not the main verb. It is being used like an adjective before ay.

So:

• gelecek ay = next month / the coming month

This comes from the verb gelmek (to come), but here it functions as coming.

Compare:

• Ay gelecek. = The moon/month will come or more naturally just a grammatical example with gelecek as a verb
• Gelecek ay = next month with gelecek describing ay

So in your sentence, the main verb is başlayacak.

Turkish often uses gelecek (coming) with time words to mean next.

Examples:

• gelecek hafta = next week
• gelecek ay = next month
• gelecek yıl = next year

So literally, gelecek ay is something like the coming month, but in natural English we usually say next month.

Başlayacak comes from the verb başlamak, meaning to start or to begin.

It breaks down like this:

• başla- = verb stem
• -yacak / -ecek / -acak = future tense ending

Because the stem ends in a vowel, Turkish inserts a buffer y:

• başla- + -acak → başlayacak

So başlayacak means:

• he/she/it will start
• it is going to start

In this sentence, it refers to dava, so: the case/trial will start.

Turkish often leaves out subject pronouns when they are already clear from the context.

In this sentence, the subject is explicitly stated as dava, so there is no need for o.

• Dava gelecek ay başlayacak. = The case will start next month.

Adding o would usually be unnecessary here.

Turkish does not have a word exactly like English the.

So dava can mean:

• a case
• the case

The exact meaning depends on context.

In a sentence like this, English usually needs the if both speaker and listener know which legal case is being discussed. Turkish does not mark that the same way.

Because Turkish often uses bare time expressions without a case ending when talking about when something happens.

So:

• gelecek ay = next month
• yarın = tomorrow
• gelecek hafta = next week

You can sometimes see -da/-de with time expressions, but it changes the feel a bit and is often more specific or contrastive. For basic statements like this, gelecek ay is the normal choice.

So:

• Dava gelecek ay başlayacak. = the normal, natural way to say it

Yes. Dava is the subject.

The sentence structure is roughly:

• Dava = subject
• gelecek ay = time expression
• başlayacak = verb

So the sentence means that the case/trial is the thing that will begin next month.

The verb usually comes at the end in Turkish, so başlayacak staying last is the most neutral pattern.

This sentence has a very natural order:

• Dava gelecek ay başlayacak.

But Turkish word order is flexible, and you can move things around for emphasis. For example:

• Gelecek ay dava başlayacak.
  This puts more focus on next month.

The most neutral structure is still the one you were given.

It can mean both.

Turkish future tense with -acak / -ecek often covers meanings that English expresses with both:

• will start
• is going to start

Which English version sounds best depends on context. In this sentence, either could work, but will start next month is the most straightforward translation.

A rough pronunciation guide:

• dava ≈ da-va
• gelecek ≈ geh-leh-JECK
• ay ≈ like English eye
• başlayacak ≈ bash-la-ya-JACK

A few useful letter notes:

• ş = sh
• ç = ch
• c = j as in jam

So:

• başlayacak has ş = sh
• gelecek ends with ç = ch-like sound, though in this word the final spelling is k, not ç; the c in the middle sounds like English j

If you want to sound natural, make sure the final verb başlayacak is clearly pronounced, since Turkish sentences often build toward the verb at the end.