Mi ekkoleras, kiam oni mensogas al mi.

The prefix ek- usually means to begin suddenly or to start doing something.

So:

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

In this sentence, Mi ekkoleras means something like I get angry or I become angry.

Because it is made from:

• ek-
  • koleras

When the prefix ends in k and the next part begins with k, both stay. So ekkoleras is completely normal spelling.

You pronounce both parts clearly, but in normal speech it will sound like a long or strong k sound.

There is a difference in meaning:

• Mi koleras = I am angry
• Mi ekkoleras = I get angry / I become angry

So ekkoleras focuses on the change into anger, not just the state of already being angry.

Kiam means when.

It introduces a time clause:

• kiam oni mensogas al mi = when people lie to me / when someone lies to me

So the whole sentence means that this is what happens when that situation occurs.

Oni is an indefinite pronoun. It often means:

• one
• people
• someone
• they in a general sense

In natural English, oni mensogas al mi would usually be translated as:

• people lie to me
• someone lies to me
• I am lied to

It does not refer to one specific person.

Because the verb mensogi works with al for the person who is lied to.

So:

• mensogi = to lie
• mensogi al iu = to lie to someone

That means:

• al mi = to me

You do not use the direct object ending -n here, because me is not the direct object of the verb.

The dictionary form is mensogi, meaning to lie.

Breaking down mensogas:

• mensog- = the root, related to lying / falsehood
• -as = present tense

So mensogas means lies or is lying, depending on context.

Not necessarily. In Esperanto, -as is the present tense, but it can also express:

• something happening now
• a habit
• a general truth
• something that regularly happens

In this sentence, the meaning is usually more general:

• I get angry when people lie to me

That sounds like a habitual or repeated reaction, not only one event happening at this exact moment.

Because kiam oni mensogas al mi is a subordinate clause.

Esperanto often uses commas to separate the main clause from a subordinate clause:

• Mi ekkoleras, kiam oni mensogas al mi.

This is very common and standard punctuation.

Yes, Esperanto word order is fairly flexible, as long as the grammar stays clear.

For example, you could also say:

• Kiam oni mensogas al mi, mi ekkoleras.

That means the same thing, but it starts with the when clause instead.

The original version is probably the most straightforward if you want to emphasize I get angry first.

Grammatically, it is closest to English one, but in natural translation it is often better rendered as they, people, or someone, depending on context.

So although oni can correspond to formal English one, native English speakers usually understand it more naturally as a general human subject:

• when people lie to me
• when someone lies to me

A simple pronunciation guide would be:

Mi ek-ko-LE-ras, KI-am O-ni men-SO-gas al mi.

A few notes:

• Esperanto stress is almost always on the second-to-last syllable
• kiam has two syllables: KI-am
• mensogas has stress on SO
• ekkoleras has stress on LE

Also remember:

• j sounds like English y
• g is always hard, as in go
• each vowel is pronounced clearly

Yes. That is a very good way to feel the meaning of ekkoleras.

The sentence suggests a repeated reaction:

• when that happens, anger begins

So depending on style, you might translate it as:

• I get angry when people lie to me
• I start to get angry when people lie to me
• I become angry when someone lies to me

All of those capture the basic idea.