La lifto ne funkcias, do mi iras al ĉambro numero dek du per la ŝtuparo.

Yes—Esperanto often borrows international words, and lifto is a normal word for elevator/lift.

A few useful points:

• lifto is common and easy to recognize.
• Some speakers also use elevilo.
• Esperanto vocabulary comes from several European sources, so sometimes a word may look more British, more Romance, or more generally international.

So lifto is not strange Esperanto; it is a standard noun.

They show the basic part of speech.

• -o = noun
  So lifto, ĉambro, numero, and ŝtuparo are nouns.
• -as = present tense verb
  So funkcias means works / is working, and iras means go / am going.

This is one of the most helpful things in Esperanto: the endings make grammar very predictable.

In Esperanto, ne normally goes right before the word or phrase it negates.

So:

• la lifto ne funkcias = the elevator does not work

That is the normal position. You will very often see:

• mi ne iras = I am not going
• li ne venas = he is not coming

So ne funkcias is exactly what you should expect.

Do means so, therefore, or thus.

It introduces a result or conclusion:

• La lifto ne funkcias, do mi iras...
• The elevator is not working, so I am going...

A useful comparison:

• ĉar = because, gives the reason
• do = so/therefore, gives the result

So here:

• reason: the elevator does not work
• result: I go to room 12 by the stairs

Esperanto often uses the simple present -as in places where English uses either:

• simple present
• present progressive
• sometimes a near-future sense

So mi iras can naturally mean:

• I go
• I’m going

In this sentence, it sounds like the speaker is going now, so mi iras is perfectly natural.

If you wanted a clear future meaning, you could say:

• mi iros = I will go

But here the present tense fits the situation well.

Al means to or toward, and it marks the destination.

So:

• mi iras al ĉambro numero dek du = I am going to room number 12

This is the normal way to show where someone is going.

You should not say:

• mi iras ĉambro numero dek du

because iri normally needs a destination phrase such as:

• al la ĉambro = to the room
• hejmen = homeward/home
• en la ĉambron = into the room

Here al is the simplest and most direct choice.

Both can be possible, but the version without la is very natural when the room number functions almost like a label: room 12.

So:

• al ĉambro numero dek du = to room number 12
• al la ĉambro numero dek du = to the room number 12

The version with la can sound a bit more specific or more explicitly definite. The version without la often feels like English to room 12, where the number identifies it sufficiently.

So the sentence as given is normal.

After numero, Esperanto uses a cardinal number:

• numero dek du = number 12

That is different from an ordinal:

• dekdua = twelfth

So these are not exactly the same idea:

• ĉambro numero dek du = room number 12
• la dekdua ĉambro = the twelfth room

Sometimes they might refer to the same real-world room, but grammatically they express different things:

• numero dek du = the label or number
• dekdua = the position in an ordered sequence

Per means by means of, via, or using.

So:

• per la ŝtuparo = by the stairs / via the staircase / using the stairs

As for ŝtuparo, that word means staircase or a flight/set of stairs. It is a collective noun:

• ŝtupo = a single step
• ŝtuparo = a whole staircase / stairway / stairs

English often uses the plural stairs, but Esperanto commonly uses the singular ŝtuparo for the whole structure. That is completely normal.

Because the staircase is understood as a specific one—the stairs available in that building or situation.

Esperanto uses la not only for things already mentioned, but also for things that are clear from context.

So here:

• the elevator is not working
• therefore the speaker uses the stairs

That makes per la ŝtuparo very natural.

Without la, it would sound more general and less tied to the immediate situation.

The two special consonants here are:

• ĉ = ch as in church
• ŝ = sh as in ship

So:

• ĉambro sounds roughly like CHAM-bro
• ŝtuparo sounds roughly like shtu-PA-ro

A few more pronunciation tips:

• Stress in Esperanto normally falls on the second-to-last syllable.
• So:
  • LIF-to
  • funk-CI-as
  • I-ras
  • ĉAM-bro
  • nu-ME-ro
  • ŝtu-PA-ro

That regular stress pattern is one of the nice things about Esperanto pronunciation.