Αύριο θέλω να υποβάλω την αίτηση, αλλά μου λείπει ένα δικαιολογητικό.

Greek word order is quite flexible, so Αύριο can go at the beginning to set the time frame right away: Tomorrow, I want to submit the application...

You could also say:

Θέλω να υποβάλω την αίτηση αύριο...

Both are grammatical, but putting Αύριο first gives it a little more emphasis.

This is a very common Greek pattern:

θέλω + να + verb

It means I want to ...

So:

• θέλω = I want
• να υποβάλω = to submit

Literally, the structure is closer to I want that I submit, but in natural English we translate it as I want to submit.

This is about aspect, which is very important in Greek.

• υποβάλλω = imperfective form
• υποβάλω = perfective form

After να, Greek often uses one of these two forms depending on how the action is viewed.

Here, να υποβάλω presents the action as a single complete event: submitting the application once. That is why υποβάλω is used.

If you used να υποβάλλω, it would suggest something more ongoing, repeated, or process-like, which does not fit as well here.

Because θέλω να υποβάλω does not simply mean I will submit. It means I want to submit.

So the speaker is expressing a wish, intention, or plan, not just a neutral future fact.

Compare:

• Αύριο θέλω να υποβάλω την αίτηση. = Tomorrow I want to submit the application.
• Αύριο θα υποβάλω την αίτηση. = Tomorrow I will submit the application.

Both can refer to the future, but they do not mean exactly the same thing.

Την αίτηση is the direct object of υποβάλω, so it appears in the accusative case.

The noun is:

• η αίτηση = the application (nominative)
• την αίτηση = the application (accusative)

Because the verb υποβάλω is acting on the application, Greek uses the accusative.

The dictionary form is:

η αίτηση = application / request

It is a feminine noun.

Common forms:

• η αίτηση = nominative singular
• την αίτηση = accusative singular
• της αίτησης = genitive singular

In this sentence, την αίτηση is used because it is the object of the verb.

Literally, it means something like:

to me is missing

Greek often expresses this idea differently from English. Instead of saying I am missing a document, Greek says:

μου λείπει ένα δικαιολογητικό

That is, a document is missing to me.

Natural English translations are:

• I’m missing a supporting document
• I lack a supporting document
• One required document is missing

Because μου here means to me / for me, not me as a direct object.

With λείπει, the person affected is usually expressed with a weak genitive pronoun:

• μου = to me / my
• σου = to you / your
• του / της = to him/her, his/her

So:

• μου λείπει = is missing to me
• σου λείπει = is missing to you

με would be a direct object pronoun, and that is not the structure used here.

Because the grammatical subject is ένα δικαιολογητικό, which is singular.

In Greek, the thing that is missing is the subject of the verb.

So:

• μου λείπει ένα δικαιολογητικό = one document is missing
• μου λείπουν δύο δικαιολογητικά = two documents are missing

The verb agrees with δικαιολογητικό, not with μου.

In everyday administrative Greek, δικαιολογητικό usually means a supporting document, required document, or piece of paperwork that proves something.

For example, it could be:

• an ID copy
• a certificate
• a tax paper
• proof of address

So in this sentence, ένα δικαιολογητικό means one required supporting document.

Because δικαιολογητικό is a neuter singular noun, and ένα is the neuter singular form of the indefinite article a / one.

So:

• ένας = masculine
• μία / μια = feminine
• ένα = neuter

Since δικαιολογητικό is neuter, it takes ένα.

Αλλά means but.

It connects the two parts of the sentence:

• Αύριο θέλω να υποβάλω την αίτηση
• αλλά μου λείπει ένα δικαιολογητικό

So the full meaning is:

Tomorrow I want to submit the application, but I’m missing a supporting document.

It shows contrast: the speaker wants to submit the application, but there is a problem.

Yes. Greek allows several word orders, depending on emphasis.

For example:

• Αύριο θέλω να υποβάλω την αίτηση, αλλά μου λείπει ένα δικαιολογητικό.
• Θέλω να υποβάλω την αίτηση αύριο, αλλά μου λείπει ένα δικαιολογητικό.
• Μου λείπει ένα δικαιολογητικό, αλλά αύριο θέλω να υποβάλω την αίτηση.

These are all possible, but they put emphasis in different places. The original version sounds very natural and starts by highlighting tomorrow.

Yes, very common. υποβάλλω / υποβάλω αίτηση is the standard formal expression for:

• submit an application
• file an application

You may also see similar combinations such as:

• υποβάλλω δικαιολογητικά = submit supporting documents
• υποβάλλω δήλωση = submit a declaration/form
• υποβάλλω ένσταση = file an objection

So this is useful formal or bureaucratic Greek.

It is mostly neutral, with some vocabulary common in administrative or official contexts.

Words like:

• υποβάλω
• αίτηση
• δικαιολογητικό

are especially common in paperwork, offices, government services, universities, and applications.

The grammar itself is not overly formal, but the vocabulary belongs to the language of forms and procedures.