La rompita seruro ne plu funkcias.

Rompita means broken.

It comes from:

• romp- = the root meaning break
• -it- = the past passive participle
• -a = adjective ending

So rompita literally means having been broken or simply broken.

In this sentence, rompita describes seruro, so it functions like an adjective: the broken lock.

Rompa would mean something more like breaking or related to breaking, not broken.

Esperanto uses participles to show ideas like:

• rompanta = breaking, in the process of breaking
• rompinta = having broken
• rompata = being broken
• rompita = having been broken

Because the lock is in the state of already being broken, rompita is the correct form.

Because it is acting as an adjective.

In Esperanto:

• nouns end in -o
• adjectives end in -a
• adverbs end in -e

Here seruro is the noun, and rompita describes it, so rompita must be an adjective.

Because seruro is the subject of the sentence, not the direct object.

In La rompita seruro ne plu funkcias:

• La rompita seruro = the subject
• funkcias = the verb

The accusative -n is usually used for a direct object, but there is no direct object here. The lock is the thing doing the verb funkcias or, in this case, not functioning.

No. They are different:

• seruro = lock
• ŝlosilo = key

So this sentence is about the lock, not the key.

Ne plu means no longer, not anymore, or not any longer.

• ne = not
• plu = further, anymore, any longer

Together, ne plu funkcias means doesn’t work anymore.

This is stronger and more specific than just ne funkcias, because it suggests that it worked before, but now it does not.

Because ne plu adds the idea of a change over time.

Compare:

• La seruro ne funkcias. = The lock does not work.
• La seruro ne plu funkcias. = The lock no longer works / doesn’t work anymore.

The second sentence implies that the lock used to function, but now it has stopped.

Because the sentence describes the lock’s current condition.

• funkcias = works / functions
• ne plu funkcias = no longer works

Even though the lock was broken in the past, the sentence is talking about the present result: right now, it does not function.

They are similar, but not exactly the same.

• La seruro estas rompita. = The lock is broken.
• La rompita seruro ne plu funkcias. = The broken lock no longer works.

The first sentence states the condition directly. The second uses rompita to describe the lock and then adds another idea: it no longer functions.

So the second sentence is a bit fuller and more descriptive.

In Esperanto, adjectives can often come before or after the noun, so La seruro rompita is grammatically possible in some contexts.

However, La rompita seruro is the more normal and natural order here.

Putting the adjective before the noun is very common, especially in straightforward descriptions like this one.

La is the definite article, meaning the.

So:

• la seruro = the lock
• unu seruro = one lock / a certain single lock
• seruro = lock in a general sense

Using la shows that we are talking about a specific lock that is already known from context.

Yes, funkcii is a common verb meaning to function or to work in the sense of operating properly.

For machines, devices, systems, and similar things, it is very natural:

• La horloĝo funkcias. = The clock works.
• La komputilo ne funkcias. = The computer does not work.

For people, English often says I work, but Esperanto usually uses labori for doing work as a job. So:

• Mi laboras. = I am working.
• La maŝino funkcias. = The machine is working.

Not necessarily someone specific, but it does imply that the lock is in a broken state as the result of being broken.

Because -it- is a passive participle, the focus is on the thing affected, not on who did it.

So rompita seruro means a lock that has been broken, without saying by whom or by what.