Nakon nekoliko tjedana u novom stanu polako se navikavamo na kvart i na tiho stubište.

Because nakon means after and it requires the genitive case in Croatian.

So:

• nakon nekoliko tjedana = after several weeks

Also, nekoliko usually goes with a noun in the genitive plural, which is why you get:

• tjedana = genitive plural of tjedan (week)

So the whole phrase is built the way Croatian normally expresses after several weeks.

After nekoliko (several), Croatian normally uses the genitive plural form of the noun.

So:

• tjedan = week
• tjedana = of weeks / weeks after a quantity word like several

That is why:

• nekoliko tjedana = several weeks

This is very common in Croatian with quantity expressions.

Here u means in, referring to location, not motion. When u expresses location, it takes the locative case.

So:

• stan = apartment / flat
• u stanu = in the apartment
• u novom stanu = in the new apartment

The adjective also changes to match the noun:

• novi stan = new apartment
• u novom stanu = in the new apartment

Navikavati se means to get used to or to become accustomed to.

In this sentence:

• navikavamo se = we are getting used to

It is the 1st person plural present tense form:

• ja se navikavam = I am getting used to
• mi se navikavamo = we are getting used to

So the sentence describes an ongoing adjustment process.

Because the verb is navikavati se, not just navikavati.

In Croatian, many verbs are used with se, and learners often call them reflexive verbs, although the meaning is not always literally reflexive in English.

So:

• navikavati se na nešto = to get used to something
• naviknuti se na nešto = to get used to something / become used to something

You should learn this verb together with se as a unit:

• navikavati se na

This is about aspect.

Croatian has:

• navikavati se = imperfective
• naviknuti se = perfective

Here, navikavamo se shows an ongoing process:

• we are gradually getting used to...

That fits well with polako (slowly / gradually).

If you used naviknemo se, it would sound more like the action is viewed as completed or as a whole:

• we get used to

So the imperfective form is more natural here.

Because the verb navikavati se takes the preposition na.

The pattern is:

• navikavati se na + accusative
• naviknuti se na + accusative

So:

• na kvart = to the neighborhood
• na tiho stubište = to the quiet stairwell

Even though English says get used to, Croatian uses na plus the accusative case with this verb.

Because after navikavati se na, you need the accusative, not the locative.

The noun stubište is neuter singular, and in the accusative singular, neuter nouns look the same as the nominative:

• stubište = nominative
• stubište = accusative

The adjective matches it:

• tiho stubište = quiet stairwell

If it were locative after u, then you would get:

• u tihom stubištu

But that is not what is happening here.

Croatian can either repeat the preposition or leave it implied with the second noun, depending on style and clarity.

So both of these are possible:

• na kvart i tiho stubište
• na kvart i na tiho stubište

Repeating na is very normal and often sounds clearer, especially when the two nouns are separate ideas:

• the neighborhood
• the quiet stairwell

So the repetition is not strange; it is actually quite natural.

Kvart means neighborhood, district, or part of town.

It is a very common everyday word in Croatian, especially in speech. It is a bit more informal and urban-feeling than some other possible words.

So here:

• navikavamo se na kvart = we are getting used to the neighborhood

Stubište usually means stairwell, staircase, or the shared stair area inside a building.

In a sentence about living in an apartment building, stubište usually means the common building staircase/stairwell, not just a single step or stairs in a general sense.

So:

• tiho stubište = a quiet stairwell / quiet staircase area

Polako means slowly or gradually.

Here it tells you that the process of getting used to the new environment is happening little by little:

• polako se navikavamo = we are slowly / gradually getting used to

It works very naturally with the imperfective verb navikavamo se.

Croatian word order is more flexible than English word order, but se is a clitic, which means it usually appears near the beginning of its clause, not in just any position.

So:

• polako se navikavamo sounds natural
• se polako navikavamo is not the normal placement here

The sentence also starts with a long time-and-place phrase:

• Nakon nekoliko tjedana u novom stanu...

After that, the main clause begins:

• polako se navikavamo...

So the placement of se is normal Croatian clitic behavior.

Yes. Navikavamo se is present tense.

The phrase:

• Nakon nekoliko tjedana u novom stanu

sets the situation: after spending several weeks in the new apartment, now we are in the process of getting used to things.

So the meaning is:

• after those first weeks, we are now gradually becoming accustomed to the neighborhood and the quiet stairwell

This combination is completely normal in Croatian.

Yes, but the meaning would change.

• polako se navikavamo = we are gradually getting used to it
• navikli smo se = we have gotten used to it / we got used to it

The original sentence focuses on an ongoing process. If you said navikli smo se, it would suggest the adjustment is more or less completed.

So the original version is better if you want the feeling of still adapting.