Mi ne ekkoleras rapide, sed hodiaŭ mi koleris pro la tro laŭta bruo en la oficejo.

The prefix ek- often means to start or to begin suddenly.

So:

• koleri = to be angry
• ekkoleri = to become angry, to start getting angry

That makes Mi ne ekkoleras rapide mean I don’t get angry quickly.

If you used koleras there instead, it would be less natural for this idea. The sentence is talking about how quickly someone becomes angry, not simply about the state of already being angry.

They express slightly different ideas:

• Mi ne ekkoleras rapide = I do not become angry quickly
• hodiaŭ mi koleris = today I was angry / got angry

In the second clause, koleris is a normal past-tense form of koleri. It describes what happened today.

A speaker could also say hodiaŭ mi ekkoleris if they wanted to emphasize the moment of becoming angry. But koleris is perfectly natural if the point is simply that anger happened today.

Because they talk about two different kinds of time:

• Mi ne ekkoleras rapide is a general truth or habit: “I don’t get angry quickly.”
• sed hodiaŭ mi koleris refers to one specific event today: “but today I got angry / was angry.”

This is very normal in Esperanto, just like in English:

• I don’t usually get angry quickly, but today I got angry.

Rapide is an adverb, meaning quickly.

In Esperanto:

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

So:

• rapida = quick
• rapide = quickly

Here it modifies the verb ekkoleras, so the adverb form is needed:

• Mi ne ekkoleras rapide = I don’t get angry quickly

Sed means but.

It contrasts the two ideas:

• normally: Mi ne ekkoleras rapide
• exception: sed hodiaŭ mi koleris...

So sed introduces the contrast between the speaker’s usual character and what happened today.

Pro means because of, due to, or on account of.

So:

• mi koleris pro la tro laŭta bruo = I was angry because of the too-loud noise

It gives the reason for the anger.

This is a very common use of pro in Esperanto.

This is an important distinction:

• tre = very
• tro = too, excessively

So:

• tre laŭta bruo = very loud noise
• tro laŭta bruo = noise that is too loud

In the sentence, the speaker is complaining that the noise was excessively loud, not just very loud.

La means the.

Here it points to a specific noise that the speaker has in mind: the noise in the office that caused the anger.

So pro la tro laŭta bruo means because of the too-loud noise.

In Esperanto, la is often used when the thing is definite or clearly identifiable from the situation.

Laŭta means loud. It is an adjective, so it describes a noun.

Here it describes bruo:

• bruo = noise
• laŭta bruo = loud noise

Both are singular and not accusative, so both stay in their basic forms:

• laŭta
• bruo

Esperanto adjectives agree with nouns in number and case, but here there is no plural and no accusative marking.

Because that phrase is introduced by the preposition pro.

Normally, nouns after a preposition do not take -n unless there is some special reason involving direction or another special construction.

So:

• pro la tro laŭta bruo is correct
• bruon would not be needed here

The phrase is simply a prepositional phrase meaning because of the too-loud noise.

Because en here means location, not motion toward.

• en la oficejo = in the office
• en la oficejon = into the office

The sentence describes where the noise was:

• bruo en la oficejo = noise in the office

There is no movement into the office, so no -n is used.

No. Esperanto word order is flexible.

This sentence has:

• sed hodiaŭ mi koleris

But you could also see:

• sed mi koleris hodiaŭ
• sed mi hodiaŭ koleris

The version in the sentence is natural because hodiaŭ is being highlighted early: but today...

Yes, it is very natural.

It literally works like:

• Mi ne ekkoleras rapide = I do not become angry quickly

That matches the English idea I’m not quick to get angry very well.

Esperanto often expresses this kind of idea with a verb plus an adverb rather than copying the exact English structure.

Because the word is made from:

• ek-
  • koleras

When ek- is attached to a root beginning with k, both consonants remain:

• ek + koleri → ekkoleri

This is normal in Esperanto word formation. The spelling shows the parts clearly.

In Esperanto, stress normally falls on the second-to-last syllable.

So:

• ek-ko-LE-ras
• LAŬ-ta
• o-fi-CE-jo
• HO-di-aŭ
• BRU-o

This rule is very regular, which makes pronunciation much easier than in English.

Yes, that is possible, but it has a slightly different feel.

• ekkoleri = to start to be angry, to become angry
• koleriĝi = to get angry, to become angry

Both can work. In many contexts they are very close in meaning.

However, ek- often gives a sense of the beginning of an action or state, sometimes a bit more suddenly. So Mi ne ekkoleras rapide is a very good choice for I don’t get angry quickly.

Bruo is a noun meaning noise.

The ending -o marks nouns in Esperanto.

So in this sentence:

• bruo = noise
• la tro laŭta bruo = the too-loud noise

This is the thing that caused the speaker’s anger.

Yes, depending on context, it can often be understood either way.

Strictly speaking:

• koleri is to be angry
• ekkoleri is more specifically to become angry

But in real usage, mi koleris can often be translated naturally as either:

• I was angry
• I got angry

In this sentence, English might prefer I got angry, because the first clause is about not becoming angry quickly. But I was angry today because of the noise is also possible depending on how you want to phrase it.