Hoy hablo tanto que me duele la garganta.

Because Spanish usually drops subject pronouns when the verb ending already shows who is doing the action.

• hablo = I speak / I am speaking
• The -o ending already tells you it is I

So Hoy hablo tanto... is perfectly natural. You could say Yo hablo tanto..., but that would usually add emphasis, as if you were contrasting yourself with someone else.

Hoy means today, and putting it first sets the time right away.

• Hoy hablo tanto que me duele la garganta. = neutral and very natural
• Hablo tanto hoy que me duele la garganta. = possible, but the focus feels a little different

Spanish word order is flexible, and beginning with a time expression like hoy is very common.

Tanto que means so much that.

It creates a result clause:

• Hablo tanto = I talk so much
• que me duele la garganta = that my throat hurts

So the structure is:

• [action/intensity] + tanto + que + [result]

Examples:

• Trabaja tanto que está agotado. = He works so much that he is exhausted.
• Llueve tanto que no podemos salir. = It rains so much that we can’t go out.

Good question. Both can mean so, but they are used differently.

• tan is used before adjectives or adverbs

  • tan cansado = so tired
  • tan rápido = so quickly

• tanto is used with verbs or with nouns expressing quantity

  • hablo tanto = I talk so much
  • tengo tanto trabajo = I have so much work

Here, tanto modifies the verb hablo, so tanto is the correct form.

Spanish often uses a different structure from English with body parts and physical sensations.

Instead of saying:

• my throat hurts

Spanish commonly says:

• me duele la garganta
• literally: the throat hurts to me

This structure uses:

• an indirect object pronoun: me = to me
• the verb: duele
• the body part with the definite article: la garganta

So for body parts, Spanish often prefers:

• me duele la cabeza = my head hurts
• me duelen los pies = my feet hurt

Using mi garganta is not impossible, but it is less natural in this kind of sentence.

With body parts, Spanish very often uses:

• indirect object pronoun
  • definite article

So:

• me duele la garganta
• not usually me duele mi garganta

The me already tells you whose throat it is, so la is enough.

This is very common in Spanish:

• me duele la cabeza = my head hurts
• me lavo las manos = I wash my hands
• se rompió el brazo = he broke his arm

Because the subject of the verb is la garganta, which is singular.

In me duele la garganta:

• me is not the subject
• la garganta is the subject
• so the verb must be singular: duele

Compare:

• Me duele la garganta. = My throat hurts.
• Me duelen las piernas. = My legs hurt.

So the verb agrees with the thing that hurts, not with the person affected.

Yes, more or less. A very literal version is:

• the throat hurts to me

That sounds strange in English, but it helps explain the grammar.

Spanish often expresses physical sensations this way:

• me duele la espalda = my back hurts
• me molestan los ojos = my eyes bother me
• me pican los brazos = my arms itch

So the Spanish structure is different from English, even though the meaning is the same.

Here que means that in the structure so ... that.

• Hablo tanto que me duele la garganta.
• I talk so much that my throat hurts.

This que connects the cause/intensity with the result.

It is not a question word here, and it does not mean what.

Yes, you could, and it is grammatical.

But there is a nuance:

• Hoy hablo tanto... often sounds more general or like a simple statement about today
• Hoy estoy hablando tanto... emphasizes the action as ongoing right now

In many everyday situations, Spanish prefers the simple present where English might use am talking.

So the original sentence sounds very natural.

Yes. In Spanish, the present tense often covers both ideas, depending on context.

• Hablo español. = I speak Spanish.
• Ahora hablo con Ana. = I am talking to Ana now.
• Hoy hablo tanto... = Today I’m talking so much...

The word hoy helps show that this is about what is happening today, not just a general habit.

It is general Spanish and sounds natural in Spain as well as in most other Spanish-speaking places.

All of these are standard:

• Hoy
• hablo
• tanto que
• me duele la garganta

So a learner can safely use this sentence in Spain.