Cuando tiene una rabieta, intento hablarle despacio para que se calme.

Because Spanish often omits subject pronouns when the verb form already makes the subject clear.

• intento = I try, so yo is not needed.
• tiene could mean he/she/you (formal) has, depending on context.

So the sentence naturally leaves the subjects unstated:

• (Él/Ella/Usted) tiene una rabieta
• (Yo) intento hablarle...

This is very normal Spanish.

By itself, tiene can mean:

• he has
• she has
• you have (formal singular, usted)

So in this sentence, the exact person depends on the wider context. If you already know who the speaker is talking about, Spanish does not need to repeat it.

Una rabieta means a tantrum or a fit of anger, especially the kind children have.

In Spain, rabieta is a very common word for this. Depending on the country, learners may also hear other words such as:

• berrinche
• pataleta

But rabieta is very natural in Spain Spanish.

Because hablarle means to speak to him/her/you.

It is made up of:

• hablar = to speak
• le = to him / to her / to you (formal)

So:

• hablar = to speak
• hablarle = to speak to him/her

In this sentence, le refers to the person having the tantrum.

Le is an indirect object pronoun. Here it means:

• to him
• to her
• to you (formal)

With hablar, Spanish commonly uses an indirect object pronoun for the person you speak to:

• Le hablo = I speak to him/her
• Les hablo = I speak to them / you all (formal)

So intento hablarle despacio means I try to speak to him/her slowly.

Because despacio is an adverb, and here it describes how the speaker talks.

• despacio = slowly
• lentamente = slowly
• lento/lenta = slow, but usually as an adjective

So:

• hablar despacio = to speak slowly

You could also say hablar lentamente, but despacio is very common and natural in everyday speech.

Because para que + subjunctive is used when the action after para que has a different subject.

Here the subjects are different:

• intento = I try
• se calme = he/she calms down

So Spanish uses:

• para que se calme = so that he/she calms down

If the subject were the same, Spanish would normally use para + infinitive:

• Hablo despacio para no ponerme nervioso.
• I speak slowly so as not to get nervous.

But in your sentence, I am speaking, and someone else is calming down, so para que + subjunctive is required.

Because para que normally triggers the subjunctive when it introduces a goal, purpose, or intended result.

The speaker is expressing a purpose:

• I try to speak slowly so that he/she calms down

This is not presented as a fact; it is the intended outcome. That is why Spanish uses the subjunctive:

• se calme

Not the indicative:

• se calma ❌

It comes from the verb calmarse, which means to calm down.

So:

• calmar = to calm something / someone
• calmarse = to calm down

In the sentence:

• para que se calme = so that he/she calms down

The form calme is the present subjunctive of calmarse.

Here, se is part of the pronominal verb calmarse.

It shows that the person is becoming calm rather than calming someone else.

Compare:

• calmar a alguien = to calm someone down
• calmarse = to calm down

So:

• para que se calme = so that he/she calms down

In effect, the calming happens to that person themself.

Because the sentence describes a habitual or repeated situation:

• Whenever he/she has a tantrum, I try to speak to him/her slowly...

In Spanish, when talking about things that generally happen, cuando often goes with the present tense:

• Cuando llega, comemos.
• When he arrives / Whenever he arrives, we eat.

So cuando tiene una rabieta means when/whenever he/she has a tantrum.

In this sentence, it most naturally means whenever.

Because both verbs are in the present and the sentence describes a repeated pattern, the sense is:

• Whenever he/she has a tantrum, I try to speak to him/her slowly...

A direct English translation may still use when, but the meaning is clearly habitual.

Yes, you could say something like:

• intento hablar con él/ella despacio

But it is not exactly the same emphasis.

• hablarle focuses on speaking to that person
• hablar con él/ella focuses more on speaking with that person

In your sentence, hablarle despacio is very natural and fits the idea of addressing someone calmly.

Not necessarily, but una rabieta very often suggests a child's tantrum.

You can use it for adults too, sometimes humorously or critically, but the most common association is with children.

So many learners would naturally understand the sentence as something like:

• When he/she has a tantrum, I try to speak to him/her slowly so that he/she calms down.

Because the speaker is describing what they usually do in that situation.

So the sentence has a general, repeated meaning:

• When/Whenever that happens, I try to do this

If it referred to one specific past situation, the tense would change, for example:

• Cuando tuvo una rabieta, intenté hablarle despacio para que se calmara.
• When he/she had a tantrum, I tried to speak to him/her slowly so that he/she would calm down.