A mi hermano le encantan las salchichas, pero yo prefiero un filete pequeño con ensalada.

Because encantar works like gustar.

In this structure, the thing that is pleasing or delightful becomes the grammatical subject, and the person who experiences that feeling is marked indirectly.

So:

• las salchichas = the thing that causes delight
• a mi hermano = to my brother
• le = to him
• encantan = delight / are loved by

A very literal version would be:

Sausages delight my brother.

Natural English translation: My brother loves sausages.

So Spanish is not saying my brother delights sausages. It is saying sausages delight my brother.

Yes, they both point to the same person, but they do different jobs.

• le is the indirect object pronoun required by the verb pattern.
• a mi hermano adds clarity or emphasis.

This is very common with gustar, encantar, interesar, and similar verbs.

So:

• Le encantan las salchichas = He loves sausages
• A mi hermano le encantan las salchichas = My brother loves sausages

The longer version is often used:

• to make clear who le refers to
• to emphasize that person
• to contrast with someone else

In this sentence, it helps set up the contrast with pero yo...

Because the verb agrees with las salchichas, which is plural.

With gustar-type verbs, the verb agrees with the thing liked/loved, not with the person.

Compare:

• Me encanta la música. = I love music.
  
  • la música is singular, so encanta
• Me encantan las salchichas. = I love sausages.
  
  • las salchichas is plural, so encantan

So in your sentence:

• las salchichas = plural
• therefore encantan

In Spanish, general statements about things people like often use the definite article.

So Spanish commonly says:

• Me gustan las manzanas. = I like apples.
• Le encanta el chocolate. = He loves chocolate.
• Nos gustan los perros. = We like dogs.

English often drops the article in these cases, but Spanish usually keeps it.

So:

• las salchichas = sausages in a general sense, not necessarily some specific sausages on the table

This is one of the most common differences between English and Spanish.

Yes, prefiero already means I prefer, so yo is not grammatically necessary.

Spanish often omits subject pronouns because the verb ending already shows the subject.

But yo is added here for emphasis or contrast:

• A mi hermano le encantan las salchichas, pero yo prefiero...

This means something like:

• My brother loves sausages, but I prefer...

The yo helps underline the contrast between my brother and I.

No. Preferir works more like a normal English verb.

In the sentence:

• yo prefiero un filete pequeño con ensalada

the subject is yo, and the object is un filete pequeño con ensalada.

So this is a more direct structure:

• I prefer a small steak with salad.

That is different from encantar, where the thing liked is the grammatical subject:

• A mi hermano le encantan las salchichas.

So one useful contrast is:

• encantar: Sausages delight my brother
• preferir: I prefer a steak

In Spanish, adjectives usually come after the noun.

So the normal order is:

• un filete pequeño = a small steak

Putting the adjective before the noun is possible in some cases, but it often changes the tone or emphasis and can sound more literary, subjective, or stylistic.

For a straightforward description, filete pequeño is the neutral, everyday order.

Con ensalada is a very natural way to say with salad in a food context.

It means the steak comes served with salad, without focusing on one specific salad.

Compare:

• un filete pequeño con ensalada = a small steak with salad
• un filete pequeño con una ensalada = a small steak with a salad
  
  • this sounds a bit more like one separate salad portion
• un filete pequeño con la ensalada = a small steak with the salad
  
  • this refers to a specific salad already known

So the version in the sentence is the most natural general menu-style phrasing.

In Spain, filete usually means a steak or slice/fillet of meat, depending on context.

In this sentence, un filete pequeño most naturally means a small steak.

In different contexts, filete can refer to:

• a beef steak
• a thin cut of meat
• sometimes a fillet

If you are learning Spanish from Spain, filete is a very normal word to see on menus.

Yes, salchichas is a standard word for sausages.

In Spain, the exact type can depend on context. It can refer to:

• ordinary sausages
• frankfurter-style sausages
• fresh sausages, depending on the situation

Spain also has many specific sausage words, such as:

• chorizo
• longaniza
• butifarra
• morcilla

But salchichas is a good general word for sausages.

Yes, Spanish allows some flexibility.

For example, these are possible:

• A mi hermano le encantan las salchichas.
• Las salchichas le encantan a mi hermano.

Both are grammatical, but the emphasis changes.

The original version is the most neutral if you want to introduce my brother first and then contrast him with yo.

Spanish often moves parts of the sentence around to change focus, but with gustar/encantar structures, the original order is especially common and clear.

Yes.

• Le gustan mucho las salchichas = He likes sausages a lot.
• Le encantan las salchichas = He loves sausages / He is crazy about sausages.

So encantar is stronger than gustar.

A rough scale is:

• gustar = to like
• gustar mucho = to like a lot
• encantar = to love

So the sentence uses encantan to show a strong preference.

Because with verbs like gustar and encantar, the person is introduced with a.

This is not the normal subject of the sentence. It is the person affected by the feeling, so Spanish marks that person differently:

• A María le gusta el café.
• A mis padres les encanta viajar.
• A mi hermano le encantan las salchichas.

So a mi hermano is not optional in the same way a normal subject would be. It belongs to the gustar/encantar pattern.