Sutra se prijavljujem na novu radionicu, a moja kolegica se već prijavljuje na seminar u Splitu.

Croatian often uses the present tense for a planned or expected future action, especially when a time word like sutra makes the timing clear.

So Sutra se prijavljujem... means something like Tomorrow I’m signing up... / Tomorrow I’m going to sign up...

This use is similar to English sentences like I’m leaving tomorrow. It sounds natural when the action is arranged, intended, or seen as part of a plan.

You could also say Sutra ću se prijaviti..., which is a more explicit future form.

Se is a reflexive clitic, and it is part of the verb prijaviti se / prijavljivati se, which means to sign up / to register.

So:

• prijaviti = to report, to register something/someone
• prijaviti se = to register oneself, to sign up

In English, we do not usually say register oneself, but Croatian does use this reflexive structure.

Without se, the meaning changes.

In Croatian, short unstressed words like se usually go in the second position in the clause. This is a very common word-order rule for clitics.

So:

• Sutra se prijavljujem... is natural
• Moja kolegica se već prijavljuje... is also natural

The clitic se usually comes very early in the sentence or clause, not necessarily right after the verb.

The form prijavljujem is:

• 1st person singular
• present tense
• from the imperfective verb prijavljivati se or its common present stem prijavljivati/prijavljujem se

In this sentence:

• prijavljujem se = I am signing up / I sign up
• prijavljuje se = she is signing up / she signs up

This is mainly a question of aspect, which is very important in Croatian.

• prijaviti se = perfective
  focuses on the completed act of signing up
• prijavljivati se / prijavljujem se = imperfective
  focuses more on the process, repetition, or a planned/current action

In everyday speech, both can appear in future-related contexts, but the nuance changes:

• Sutra ću se prijaviti = Tomorrow I will sign up
• Sutra se prijavljujem = Tomorrow I’m signing up / I have plans to sign up tomorrow

The preposition na is often used with events, courses, workshops, lectures, and similar activities when you are going to them or signing up for them.

So Croatian says:

• prijaviti se na radionicu
• prijaviti se na seminar
• ići na koncert
• ići na tečaj

Here na means something like for / onto / to attend, depending on the context.

Because na here expresses direction toward an event or enrollment into it, it takes the accusative case.

Because after na in this sentence, the noun is in the accusative case.

The base form is:

• nova radionica = nominative

But after na here it becomes:

• na novu radionicu = accusative

Both the adjective and the noun change:

• nova → novu
• radionica → radionicu

This is a very typical feminine singular accusative pattern.

Because this sentence is about signing up for a seminar, so the idea is directional: toward participation in the event. That requires accusative after na.

So:

• na seminar = accusative
• na seminaru = locative, meaning at the seminar

Compare:

• Prijavljujem se na seminar. = I’m signing up for the seminar.
• Predajem na seminaru. = I teach at the seminar.

Also, seminar is a masculine noun, and for many masculine inanimate nouns, the accusative singular looks the same as the nominative:

• seminar → seminar

U Splitu is in the locative case because it means in Split as a location.

With u:

• u Split would suggest movement into/toward a place
• u Splitu means being located there

Here the seminar is located in Split, so Croatian uses u Splitu.

This is very common:

• u Zagrebu
• u Rijeci
• u Splitu

Već usually means already.

Here it suggests that the colleague is signing up already, perhaps earlier than expected or before the speaker does.

So it adds a nuance like:

• she has already started the process
• she is doing it sooner than the speaker
• the action is underway now

It often gives a sense of contrast with the first clause.

A often connects two clauses with a slight contrast or comparison, while i simply means and.

In this sentence, a works well because the speaker is comparing two similar actions:

• I’m signing up tomorrow
• my colleague is already signing up

So a feels like:

• and meanwhile
• while
• whereas
• and, by contrast

It is not a strong opposition like ali (but), but it does signal a contrast in timing or perspective.

Yes, Croatian word order is fairly flexible, but not completely free. You can move things around for emphasis, topic, or style.

For example, these are possible with different emphasis:

• Sutra se prijavljujem na novu radionicu...
• Na novu radionicu se prijavljujem sutra...
• Moja se kolegica već prijavljuje na seminar u Splitu...

However, some positions sound more natural than others, and the clitic se still has to follow the usual clitic-placement rules.

The original sentence is neutral and natural.

Moja kolegica means my colleague. The possessive adjective moja agrees with kolegica in gender, number, and case.

It is not always strictly necessary if the context is obvious, and a speaker could simply say kolegica. But using moja makes the relationship clear and sounds very natural.

Forms here:

• moj = masculine
• moja = feminine
• moje = neuter

Since kolegica is feminine singular, the correct form is moja.

Yes. Kolegica refers to a female colleague.

The masculine form is kolega.

So:

• moj kolega = my male colleague
• moja kolegica = my female colleague

This is a normal gender distinction in Croatian nouns referring to people.

Because a is joining two independent clauses:

• Sutra se prijavljujem na novu radionicu
• moja kolegica se već prijavljuje na seminar u Splitu

In Croatian, a comma is normally used before conjunctions like a, ali, and often before clauses of this type. So the comma here is standard punctuation.