Hieraŭ la vento rompis unu fenestron, sed hodiaŭ mia fratino provas ripari ĝin.

Because hieraŭ is an adverb of time, and Esperanto often puts time words near the beginning of a sentence or clause. This sets the time frame right away. In this sentence, Hieraŭ contrasts nicely with hodiaŭ later on.

Also, Esperanto word order is fairly flexible, so starting with a time word is very normal.

Rompis is made of:

• romp- = the word root
• -is = past tense

So -is shows that the action happened in the past.

A useful Esperanto feature is that verbs do not change for person:

• mi rompis
• vi rompis
• li rompis
• ili rompis

They all use the same past-tense ending -is.

The ending -n marks the direct object in Esperanto.

Here, fenestron is the thing affected by the action of breaking. The wind did the action, and the window received the action.

So:

• la vento = subject
• unu fenestron = direct object

That is why fenestron has -n, but vento does not.

Yes, Esperanto has no indefinite article like English a/an.

So fenestron by itself could already mean a window.

Adding unu usually emphasizes the number one:

• exactly one window
• not two or several

So unu fenestron sounds more specific than just fenestron.

La is the definite article, like English the.

In la vento, it is used because the speaker is referring to the wind as a definite thing in the situation.

But mia is a possessive adjective, and in Esperanto possessives normally replace the article. So you say:

• mia fratino
• not normally la mia fratino

This works much like English: my sister, not the my sister.

Because mia fratino is the subject of the second clause.

She is the one doing the action of provas. The thing receiving the action is ĝin, so that is the object.

Compare:

• mia fratino provas = my sister is trying
• mi vidas mian fratinon = I see my sister

In the second example, fratinon gets -n because it is the object.

Because provas ripari means that she is trying to repair it, not necessarily succeeding yet.

• provas = tries / is trying
• ripari = to repair

If the sentence said mia fratino riparas ĝin, that would mean she is repairing it, without the idea of trying being emphasized.

Because after a verb like provas, the next verb usually stays in the infinitive form.

So:

• provas ripari
• volas iri
• povas veni
• devas labori

Only the first verb is conjugated here. The second verb names the action being attempted, wanted, possible, and so on.

Because ĝin is the object form of ĝi.

Just like nouns can take -n as direct objects, pronouns can too.

So:

• ĝi = it
• ĝin = it as a direct object

In this sentence, ĝin refers back to fenestron, the thing the sister is trying to repair.

No. Ĝi/ĝin does not mean feminine or masculine.

Esperanto usually does not assign grammatical gender to things like a window. So a window is naturally referred to as ĝi or ĝin.

The female person in the sentence is shown by fratino. If you replaced mia fratino with a pronoun, you would use ŝi or ŝin, not ĝi.

Yes, to a degree.

For example, Esperanto could also say something like:

La vento hieraŭ rompis unu fenestron, sed hodiaŭ mia fratino provas ripari ĝin.

That is still grammatical. Esperanto allows this because endings like -n help show what is the subject and what is the object.

However, different word orders can change the emphasis. The original version puts strong focus on the contrast between hieraŭ and hodiaŭ.

Because sed joins two independent clauses here:

• Hieraŭ la vento rompis unu fenestron
• hodiaŭ mia fratino provas ripari ĝin

Using a comma before sed is normal and helps show the break between the two complete thoughts.