Ni sidas proksime al la fenestro en la kafejo.

Sidas means are sitting or sit. It tells you the specific action or posture.

• Ni sidas = We are sitting / We sit
• Ni estas = We are (just existence or identity)

So if you want to say where the people are seated, sidas is the natural verb.

The verb stem is sid-, which means sit.

The ending -as marks the present tense in Esperanto. So:

• sidas = sit / am sitting / are sitting
• sidis = sat / were sitting
• sidos = will sit / will be sitting

Esperanto verbs do not change for person, so:

• mi sidas = I sit / I am sitting
• vi sidas = you sit / you are sitting
• ni sidas = we sit / we are sitting

Because proksime is an adverb, and here it describes how/where we sit.

• proksima = near, as an adjective describing a noun
  
  • la proksima fenestro = the nearby window
• proksime = near(ly), as an adverb
  
  • Ni sidas proksime = We are sitting nearby

In this sentence, Esperanto uses the pattern proksime al = near to / close to.

So:

• Ni sidas proksime al la fenestro = We are sitting near the window

In Esperanto, proksime often goes with al when you say what something is near.

• proksime al la fenestro = near the window
• literally: near to the window

This is a very common pattern:

• proksime al la stacidomo = near the station
• proksime al mia domo = near my house

English usually says just near the window, but Esperanto commonly says proksime al la fenestro.

Because la fenestro is not the direct object of the verb sidas.

The -n ending is mainly used for:

1. direct objects
   
   • Mi vidas la fenestron = I see the window
2. motion toward a place in some expressions
   
   • Mi iras en la kafejon = I go into the café

But here, la fenestro is part of the prepositional phrase al la fenestro. Prepositions normally prevent the noun from taking -n.

So:

• proksime al la fenestro = near the window
  not al la fenestron

In this sentence, la means the, just as in English.

• la fenestro = the window
• la kafejo = the café

Esperanto uses la when the speaker has a specific thing in mind, or when the context makes it clear which one is meant.

In many situations, English and Esperanto match here:

• near the window
• in the café

You could also say:

• Ni sidas proksime al fenestro en kafejo

but that sounds less natural in most ordinary contexts, because it means something more like near a window in a café rather than a specific, known setting.

Yes. kafejo is built from kafo (coffee) plus the suffix -ej-, which means place for.

So:

• kafo = coffee
• kafejo = coffee place, café

This suffix is very useful in Esperanto:

• lerni = to learn → lernejo = school
• dormi = to sleep → dormejo = dormitory / sleeping place
• kuiri = to cook → kuirejo = kitchen

So kafejo is a very transparent word once you know -ej-.

Because it adds another piece of location information: the sitting happens in the café.

The sentence has two place expressions:

• proksime al la fenestro = near the window
• en la kafejo = in the café

Putting en la kafejo at the end is natural and easy to follow. It gives the broader setting after the more specific location.

You could change the word order without changing the basic meaning much, for example:

• En la kafejo ni sidas proksime al la fenestro.
• Ni sidas en la kafejo proksime al la fenestro.

Esperanto word order is fairly flexible, but the original order sounds very natural.

In practice, most people will understand it as part of the whole scene: we are sitting near the window, in the café.

Since both the sitting and the window are located in the café, there is no real problem here. Esperanto often allows this kind of natural, context-based interpretation.

If you wanted to make it extra clear, you could say:

• Ni sidas en la kafejo, proksime al la fenestro.

But the original sentence is already clear and idiomatic.

Yes, and it is very common.

• ĉe la fenestro = at the window / by the window
• proksime al la fenestro = near the window

These are similar, but not always identical:

• ĉe la fenestro often suggests being right by it
• proksime al la fenestro means nearby, possibly a little less directly adjacent

So Ni sidas ĉe la fenestro en la kafejo would also be a very natural sentence.

It can mean either one, depending on context.

Esperanto -as does not force a distinction between:

• simple present: We sit
• present progressive: We are sitting

So Ni sidas can mean:

• We are sitting (most likely in this sentence)
• We sit (in a habitual or general sense, if the context supports that)

Usually the situation makes the intended meaning obvious.

Only because it begins the sentence.

• Ni = we
• ni = we

Esperanto capitalizes words the same way English does at the beginning of a sentence and in proper names. So here Ni is capitalized simply because it is the first word.

A rough English-friendly pronunciation is:

nee SEE-dahs prok-SEE-meh ahl lah feh-NES-troh en lah kah-FEY-yoh

A few helpful points:

• Ni sounds like nee
• sidas has stress on SI
• proksime has stress on SI
• fenestro has stress on NES
• kafejo has stress on FE

In Esperanto, the stress is almost always on the second-to-last syllable, which makes pronunciation very regular.