Ta kamienica jest stara, ale jej domofon działa dobrze.

Because kamienica is a feminine noun in Polish. The demonstrative this must agree with the noun’s gender:

• ten = masculine
• ta = feminine
• to = neuter

So:

• ta kamienica = this building / this tenement house

The adjective also has to agree in gender, which is why you later get stara and not stary.

Kamienica usually means a traditional multi-storey town building, often an older urban apartment building or tenement house. It is more specific than building in general.

So depending on context, English translations might be:

• tenement house
• apartment building
• old townhouse
• sometimes just building

In this sentence, it suggests an older residential building.

Because stary / stara / stare must agree with the noun it describes.

Since kamienica is feminine, the adjective must also be feminine:

• masculine: stary
• feminine: stara
• neuter: stare

So:

• ta kamienica jest stara = this building is old

In the present tense, Polish normally does use jest when saying something like is old.

So:

• Ta kamienica jest stara = This building is old

Polish sometimes omits jest in certain styles or very informal situations, especially in headlines or poetic language, but for normal standard sentences like this, jest is the expected form.

Because ale means but, and in Polish it normally introduces a new clause, so it is preceded by a comma.

• Ta kamienica jest stara, ale jej domofon działa dobrze.

This is very standard Polish punctuation.

Here jej means its or more literally her, referring back to the feminine noun kamienica.

Polish possessive pronouns agree with the owner, not with the thing owned:

• jego = his / its for masculine or neuter owners
• jej = her / its for feminine owners

Since kamienica is feminine, you use:

• jej domofon = its intercom

Even though in English we usually say its, Polish uses the same form as her when the owner is a feminine noun.

In this sentence, jej is being used as a possessive pronoun before a noun: jej domofon.

This form jej does not change for the gender or number of the thing owned. It stays the same:

• jej domofon = her/its intercom
• jej drzwi = her/its door
• jej okna = her/its windows

So the important thing is that the owner is feminine, not that domofon is masculine.

Because domofon is the subject of the second clause:

• jej domofon działa dobrze = its intercom works well

Subjects normally appear in the nominative case, which is the dictionary form. So:

• domofon = nominative singular

Likewise, kamienica is nominative in the first clause because it is also the subject there.

Domofon is the entry-phone/intercom system used at the entrance of a building, especially apartment buildings.

Possible English equivalents are:

• intercom
• entry phone
• door-entry system

So jej domofon działa dobrze means the building’s entry intercom works properly.

Because działa dobrze means works well / functions properly, which is the natural thing to say about a device.

• działa dobrze = it functions well
• jest dobry = it is good

For a machine or system, Polish often uses działać when talking about whether it is functioning:

• Telefon działa dobrze. = The phone works well.
• Domofon działa dobrze. = The intercom works well.

So działa dobrze focuses on performance, not general quality.

Because dobrze is an adverb, and it modifies the verb działa.

• dobry = good (adjective, describes a noun)
• dobrze = well (adverb, describes a verb)

Here we are describing how the intercom works:

• działa dobrze = works well

Not:

• dobry domofon = a good intercom

Not completely. Polish word order is more flexible than English, although the original sentence is the most neutral and natural:

• Ta kamienica jest stara, ale jej domofon działa dobrze.

You could also hear variations like:

• Ta kamienica jest stara, ale domofon jej działa dobrze.

But that sounds less neutral and may put unusual emphasis on jej. For learners, the original version is best.

Yes, but it means something slightly different structurally.

• Ta kamienica jest stara. = This building is old.
• Ta stara kamienica... = This old building...

In the original sentence, stara is part of the predicate after jest. If you move it before the noun, it becomes a regular attributive adjective.

So both are correct, but they are different sentence structures.

A rough approximation is yay or yey, though exact pronunciation depends on accent and carefulness.

A few quick pronunciation notes for the whole sentence:

• ta ≈ tah
• kamienica ≈ ka-mye-NI-tsa
• jest ≈ yest
• stara ≈ STA-ra
• jej ≈ yay / yey
• domofon ≈ do-MO-fon
• działa ≈ DJA-wa or JWA-wa depending on how you hear the cluster
• dobrze ≈ DOB-zhe

The tricky parts for English speakers are often jej, działa, and dobrze.

Yes. This is very important in Polish.

Polish grammatical gender does not always match natural gender. A noun like kamienica is grammatically feminine, so when referring back to it, Polish uses the feminine possessive form:

• jej domofon = its intercom

In English, we do not usually call a building her, but Polish grammar does not work the same way here. So jej can absolutely mean its when it refers to a feminine noun.