Diga lo que diga mi hermano, voy a seguir estudiando español.

Because this is a very common Spanish pattern:

subjunctive + lo que + subjunctive

So diga lo que diga mi hermano means something like whatever my brother says.

The first diga introduces the pattern, and the second diga is the actual verb connected to mi hermano.

You will see the same structure in many similar expressions:

• Haga lo que haga = whatever he/she does
• Venga quien venga = whoever comes
• Pase lo que pase = whatever happens

It sounds repetitive in English, but in Spanish it is normal.

Because this construction expresses indifference, concession, or uncertainty: the speaker is saying the result will be the same no matter what the brother says.

That is why Spanish uses the subjunctive here.

So diga lo que diga mi hermano is not just reporting what the brother says. It means:

• regardless of what he says
• no matter what he may say
• whatever he says

This is one of the standard environments where the subjunctive appears.

Here lo que means what or whatever it is that.

In this pattern, lo que links the two parts of the concessive expression:

• diga lo que diga = say whatever he may say

You do not need to translate lo separately in a very literal way here. It is part of the fixed structure.

Compare:

• No entiendo lo que dices = I don’t understand what you are saying
• Diga lo que diga = whatever he says

So the exact nuance depends on the structure.

Because in Spanish, the subject can often appear after the verb, especially in expressions like this.

So:

• Diga lo que diga mi hermano = natural
• Diga lo que mi hermano diga = also grammatical, but different in feel and less idiomatic here
• Mi hermano diga lo que diga = possible in some contexts, but not the most neutral version

In this sentence, putting mi hermano after the second diga sounds very natural and highlights the fixed pattern diga lo que diga first.

Yes, or at least a very common fixed-style pattern.

It belongs to a broader group of concessive structures used to mean no matter... or whatever...:

• Diga lo que diga = whatever he/she says
• Sea como sea = however it may be / anyway
• Vaya donde vaya = wherever he/she goes
• Tengas la edad que tengas = whatever age you are

So even though you can analyse the grammar, it is also useful to learn diga lo que diga as a chunk.

Both are correct.

• Voy a seguir estudiando español = I’m going to keep studying Spanish
• Seguiré estudiando español = I will keep studying Spanish

The version with ir a + infinitive is very common in everyday spoken Spanish and often sounds a bit more immediate or conversational.

The future tense seguiré is also fine, but can sound slightly more formal, more definite, or simply more written depending on context.

So the original sentence sounds very natural in normal speech.

After seguir, Spanish normally uses either:

• an infinitive
• or a gerund

So both are possible:

• voy a seguir estudiando español
• voy a seguir estudiando
• voy a seguir estudiar ❌

Actually, the correct infinitive version would be:

• voy a seguir estudiando español
• voy a seguir estudiando
• voy a seguir con el estudio del español
• voy a seguir estudiando or voy a seguir con mis estudios de español

With seguir, the most common verbal patterns are:

• seguir + gerundio = keep doing
• seguir + adjective/adverb in some other uses
• seguir con + noun

In this sentence, seguir estudiando is the natural verbal expression for keep studying.

Yes, absolutely.

So these are both good:

• Diga lo que diga mi hermano, voy a seguir estudiando español.
• Diga lo que diga mi hermano, seguiré estudiando español.

The difference is mainly one of style and tone:

• voy a seguir... = a bit more conversational and immediate
• seguiré... = a bit more compact and slightly more formal or emphatic

Neither changes the basic meaning much.

Yes, it is the normal punctuation here.

The first part, Diga lo que diga mi hermano, is an introductory concessive clause. The main clause comes after it:

• Diga lo que diga mi hermano,
• voy a seguir estudiando español.

The comma helps separate the no matter what my brother says part from the main statement.

In writing, this is the expected punctuation.

Yes, exactly. It is the same kind of structure.

For example:

• Pase lo que pase, voy a seguir estudiando español.
• Diga lo que diga mi hermano, voy a seguir estudiando español.

Both mean that the speaker’s decision will not change.

This is a very useful pattern to learn because you can reuse it with many verbs:

• haga lo que haga
• diga lo que diga
• piensen lo que piensen
• venga quien venga

Yes, it sounds completely natural in Spain.

Everything in the sentence is standard and common:

• Diga lo que diga... is a normal concessive expression
• voy a seguir... is very natural in spoken Spanish
• estudiando español is the ordinary way to say studying Spanish

So a speaker from Spain would understand it immediately and would find it perfectly idiomatic.