Mi ne ŝatas flugi, sed mia fratino ĝojas, kiam ŝi sidas apud la fenestro en la aviadilo.

Esperanto endings carry a lot of grammar. In this sentence, the most important ones are:

• -as = present tense verb
  
  • ŝatas = like
  • ĝojas = is glad / rejoices
  • sidas = sits / is sitting
• -i = infinitive, like English to ...
  
  • flugi = to fly
• -o = noun
  
  • fratino = sister
  • fenestro = window
  • aviadilo = airplane
• -a = adjective-type ending
  
  • mia = my
    Possessives like mia, via, ŝia behave like adjectives in Esperanto.

Once you get used to these endings, sentences become much easier to parse.

Because Esperanto often uses ŝati + infinitive to mean to like doing something.

So:

• Mi ŝatas flugi = I like to fly / I like flying
• Mi ne ŝatas flugi = I don’t like to fly / I don’t like flying

This works much like English like to fly. Esperanto does not need a special -ing form here.

Sed means but.

It connects two contrasting ideas:

• Mi ne ŝatas flugi = I don’t like flying
• sed mia fratino ĝojas... = but my sister is happy...

Its position is very similar to English but.

Fratino is built from parts:

• frat- = sibling/brother-related root
• -in- = female suffix
• -o = noun ending

So fratino means sister.

A very common pattern in Esperanto is:

• patro = father
• patrino = mother
• frato = brother
• fratino = sister

So the sentence says mia fratino = my sister.

Ĝoji is a verb meaning to rejoice, to be glad, to feel joy.

So:

• mia fratino ĝojas = my sister is glad / happy

You could also say mia fratino estas ĝoja, which means my sister is joyful/happy. But ĝojas is very natural and often feels a bit more like describing the feeling itself.

So in this sentence, ĝojas is a perfectly normal choice.

Kiam means when.

Here it introduces a time clause:

• kiam ŝi sidas apud la fenestro... = when she sits by the window...

So the structure is:

• mia fratino ĝojas, kiam...
  my sister is happy when...

Also, kiam can be used both:

• as a question word: Kiam vi venos? = When will you come?
• as a conjunction: Mi ĝojas kiam vi venas. = I’m happy when you come.

In your sentence, it is a conjunction.

Usually Esperanto does use subject pronouns.

That is because the verb ending -as only tells you the tense, not the person. So:

• sidas could mean I sit, you sit, she sits, they sit, etc.
• The pronoun tells you who is doing it.

So:

• ŝi sidas = she sits / she is sitting

Pronouns can sometimes be omitted if the meaning is already very clear, but in normal standard Esperanto, keeping ŝi is the expected form here.

Because this phrase shows location, not movement toward something.

• apud = beside / next to
• apud la fenestro = next to the window

In this sentence, she is already sitting there:

• ŝi sidas apud la fenestro = she is sitting next to the window

No accusative -n is needed because nothing is being moved toward the window. It is a static position.

A good rule of thumb:

• location → usually no -n
• direction/motion toward → sometimes -n is used

Because en means in / inside, while sur means on / on top of.

So:

• en la aviadilo = in the airplane, inside it
• sur la aviadilo = on the airplane, on its outside surface

Since the sister is sitting by the window as a passenger, en la aviadilo is the natural choice.

La is Esperanto’s definite article, meaning the.

It is used when the noun is specific or understood from the context.

Here:

• la aviadilo = the airplane, the one they are in
• la fenestro = the window, meaning the window next to her seat / the relevant window in that situation

This sounds natural because the situation is specific.

Also remember: Esperanto has no indefinite article. There is no separate word for a/an.

Because kiam ŝi sidas apud la fenestro en la aviadilo is a subordinate clause.

Esperanto commonly uses commas to separate subordinate clauses from the main clause:

• mia fratino ĝojas, kiam ŝi sidas...

This is very normal punctuation in Esperanto.

The special letters are important:

• ŝ sounds like sh in ship
• ĝ sounds like j in jam

So:

• ŝi is pronounced roughly shee
• ŝatas starts with sha-
• ĝojas is pronounced roughly JOY-as

A few extra pronunciation tips:

• j often sounds like English y
• oj sounds like oy, so ĝo-jas gives joy-as
• Stress in Esperanto is always on the second-to-last syllable

Examples:

• a-vi-a-DI-lo
• fe-NE-stro
• ĝO-jas

Yes. Esperanto word order is fairly flexible because the endings carry so much information.

For example, you could also say:

• Kiam ŝi sidas apud la fenestro en la aviadilo, mia fratino ĝojas.

That still means the same thing: My sister is happy when she sits by the window in the airplane.

The original version is very natural, though:

• first the speaker’s opinion,
• then the contrast,
• then the condition under which the sister is happy.

Because it describes a singular noun in the basic form:

• mia fratino = my sister

Possessive words like mia can change when grammar requires it, just like adjectives:

• mia fratino = my sister
• miaj fratinoj = my sisters
• mian fratinon = my sister, as a direct object
• miajn fratinojn = my sisters, as direct objects

In this sentence, fratino is singular and not an object, so plain mia is correct.