Ni esperas, ke la trajno ne malfruos.

Ke means that and introduces a subordinate clause.

So the sentence is built like this:

• Ni esperas = We hope
• ke la trajno ne malfruos = that the train will not be late

This is very similar to English We hope that... Even though English often leaves out that, Esperanto normally keeps ke in this kind of sentence.

Because the lateness has not happened yet from the speaker’s point of view.

• malfruas = is late
• malfruos = will be late

In this sentence, the speakers are hoping about a future event, so -os is used.

It breaks down neatly into parts:

• mal- = opposite
• fru- = early
• -i would make the infinitive malfrui = to be late
• -os = future tense

So:

• frua = early
• malfrua = late
• malfrui = to be late
• malfruos = will be late

This is a very common Esperanto pattern: use mal- to create the opposite of a word.

In Esperanto, ne usually goes directly before the part it negates.

Here it negates the verb:

• la trajno malfruos = the train will be late
• la trajno ne malfruos = the train will not be late

So the placement is very straightforward and natural.

La is the definite article, meaning the.

So:

• trajno = a train / train
• la trajno = the train

The sentence is referring to a specific train that both speaker and listener can identify, so la is used.

Unlike English, Esperanto has only one article, la, and it does not change for gender, number, or case.

Because trajno is the subject of malfruos, not the direct object.

In Esperanto:

• the subject has no special ending
• the direct object usually takes -n

Here, la trajno is the thing doing the action of being late, so it is the subject.

Compare:

• La trajno malfruos. = The train will be late.
• Ni vidas la trajnon. = We see the train.

In the second sentence, trajnon gets -n because it is the direct object of vidas.

Because Esperanto normally states the subject explicitly.

• Ni = we
• esperas = hope / are hoping

Unlike languages such as Spanish or Italian, Esperanto usually does not drop subject pronouns in ordinary sentences. So Ni esperas is the normal way to say We hope.

Yes. In Esperanto, many verbs describe a state as well as an action.

So malfrui means to be late.

This is completely normal in Esperanto. You do not always need a separate verb like to be plus an adjective.

For example:

• La trajno malfruas. = The train is late.
• Li silentas. = He is silent / He keeps silent.

Esperanto often prefers this compact verbal style.

Yes, that is also grammatical.

There is a small stylistic difference:

• la trajno ne malfruos = the train will not be late
• la trajno ne estos malfrua = the train will not be late / will not be a late one

In practice, both can work, but ne malfruos is usually more direct and idiomatic here. Esperanto often prefers the simple verb malfrui rather than esti malfrua.

The given word order is the most natural:

• Ni esperas, ke la trajno ne malfruos.

Esperanto word order is fairly flexible, but not completely free. Because the grammar endings show the roles of words, some rearrangement is possible for emphasis. Still, learners should usually stick to the normal order:

• main clause first
• then ke
• then subject + ne
  • verb

So this sentence is a good model to copy.

Because ke introduces a subordinate clause, and Esperanto normally separates that clause with a comma.

So:

• Ni esperas, ke...

This is standard Esperanto punctuation. Even where English might sometimes omit punctuation or vary, Esperanto commonly uses the comma before ke.

It is a verb in the present tense.

Breaking it down:

• esper- = hope
• -as = present tense

So esperas means hope or are hoping, depending on context.

With ni, it becomes:

• Ni esperas = We hope / We are hoping

Yes, in ordinary use that is the natural equivalent.

Esperanto often expresses this idea with a single verb:

• malfrui = to be late

So instead of using a structure exactly like English will not be late, Esperanto says:

• ne malfruos = will not be late

It is simple and very common.