A veces prefiero el doblaje porque estoy cansado y no quiero leer subtítulos.

A veces means sometimes.

It is a fixed expression in Spanish:

• vez = time / occasion
• veces = times / occasions

So Spanish uses the plural idea, literally something like at times. You should learn a veces as a whole expression.

Examples:

• A veces estudio por la mañana.
• A veces no tengo ganas de cocinar.

Yes. A veces is quite flexible.

These are all natural:

• A veces prefiero el doblaje...
• Prefiero a veces el doblaje...
• Prefiero el doblaje a veces...

The most neutral and common position is at the beginning, as in your sentence. That is often where Spanish puts time expressions like a veces, hoy, normalmente, por la noche, etc.

Because preferir is a stem-changing verb.

In the present tense, the e in the stem changes to ie in most forms:

• yo prefiero
• tú prefieres
• él/ella prefiere
• nosotros preferimos
• vosotros preferís
• ellos prefieren

So prefiero is the correct I prefer form.

This kind of change is very common in Spanish:

• querer → quiero
• pensar → pienso
• sentir → siento

Spanish often leaves out subject pronouns when the verb already shows who the subject is.

Here, prefiero already tells you it means I prefer, so yo is not necessary.

You could say:

• A veces yo prefiero el doblaje...

But that usually adds emphasis, contrast, or clarity, for example:

• Yo prefiero el doblaje, pero mi hermano prefiere los subtítulos.

So in a normal statement, leaving out yo sounds very natural.

Because in Spanish, general nouns often appear with the definite article more often than they do in English.

So Spanish commonly says:

• prefiero el doblaje
• me gusta el cine
• odio el ruido
• me encantan los libros

In English, you might say I prefer dubbing, without the, but Spanish often uses el/la/los/las in these cases.

In Spain, el doblaje usually means dubbing: replacing the original spoken audio with voices in Spanish.

It can refer to dubbing in general:

• Prefiero el doblaje.

If you want to be more specific about a film or series, you could also hear:

• la versión doblada = the dubbed version
• el audio doblado = the dubbed audio

For example:

• Prefiero la versión doblada de esta película.

Your original sentence is completely natural.

Because porque is the conjunction meaning because.

Spanish distinguishes several similar-looking forms:

• porque = because
• por qué = why
• el porqué = the reason
• por que = less common combination in specific structures

In your sentence, the speaker is giving a reason, so porque is correct:

• Prefiero el doblaje porque estoy cansado.

If it were a question, you would use por qué:

• ¿Por qué prefieres el doblaje?

Because Spanish usually uses estar for temporary states or conditions, and being tired is seen as a state, not a permanent characteristic.

So:

• estoy cansado = I am tired

By contrast, ser is usually for identity, essential traits, origin, profession, and similar ideas.

This is a very common pattern:

• estoy cansado
• estoy enfermo
• estoy ocupado
• estoy contento

Saying soy cansado would not mean I am tired. It would sound like I am a tiring person or I am tiresome, which is a different idea and usually expressed more naturally as soy cansino/cansina or soy agotador/agotadora, depending on context.

Yes. Cansado agrees with the speaker.

• A man would normally say estoy cansado
• A woman would normally say estoy cansada

If the subject is plural:

• estamos cansados = we are tired
• estamos cansadas = we are tired, all female

So the ending changes to match gender and number, just like many Spanish adjectives.

Because querer is often followed directly by an infinitive.

The structure is:

• querer + infinitive

So:

• quiero leer = I want to read
• quiero comer = I want to eat
• quiero dormir = I want to sleep

When you make it negative, the no goes before the conjugated verb:

• no quiero leer

You do not need a preposition here. So no quiero leer is correct, not no quiero a leer.

Because Spanish can omit the article when talking about things in a general, non-specific way.

Here, leer subtítulos means to read subtitles in general, not necessarily a specific set of subtitles.

That is why the sentence sounds natural as:

• no quiero leer subtítulos

If you were talking about specific subtitles, the article would be more likely:

• No quiero leer los subtítulos de esta película.

So both are possible, but they mean slightly different things:

• leer subtítulos = read subtitles in general
• leer los subtítulos = read the subtitles, a specific set

Because the stress falls on tí: sub-TÍ-tu-los.

Without the accent mark, Spanish stress rules would make you pronounce it differently. The written accent shows the correct stressed syllable.

This is very common in Spanish and helps you know where to place the stress:

• película
• música
• teléfono
• subtítulos

So the accent is not optional; it is part of the correct spelling.

Yes, it is very natural in Spain.

A Spanish speaker in Spain could easily say:

• A veces prefiero el doblaje porque estoy cansado y no quiero leer subtítulos.

Some natural alternatives are:

• A veces prefiero la versión doblada porque estoy cansado y no me apetece leer subtítulos.
• A veces prefiero verla doblada porque estoy cansado.

But your original sentence is clear, correct, and idiomatic.

Yes, you could, and the meaning is very similar.

• A veces = sometimes
• Algunas veces = sometimes / some times

In everyday speech, a veces is usually shorter and more common. It sounds very natural and is probably the most usual choice here.

So both work, but a veces is the more standard, concise option in this sentence.