En lo que respecta a la legalización, hay preguntas.

It means as regards, with regard to, or when it comes to.

So En lo que respecta a la legalización introduces the topic: legalization. It is a fairly formal way to say speaking about legalization or as far as legalization is concerned.

Both are possible, but they are different expressions.

• En lo que respecta a... = as far as ... is concerned
• Respecto a... = regarding ... / with respect to ...

So:

• En lo que respecta a la legalización, hay preguntas.
• Respecto a la legalización, hay preguntas.

Both are correct. The version with En lo que respecta a sounds a bit longer and slightly more formal.

Because the subject is lo que, which is treated as singular here.

In En lo que respecta a..., the structure literally works like in that which concerns..., so Spanish uses respecta and not respectan.

This whole expression is fixed, so it is best to learn it as one chunk: En lo que respecta a...

Because the verb respectar in this expression is followed by a when introducing the thing being referred to.

So:

• respecta a la legalización
• respecta al problema
• respecta a los estudiantes

Here, a is just part of the pattern you need after this phrase.

In Spanish, general abstract nouns often take the definite article more often than in English.

So Spanish says:

• la legalización
• la educación
• la justicia

Even when English might just say legalization, Spanish often prefers la legalización.

Hay means there is or there are.

Here it means there are because preguntas is plural:

• Hay una pregunta = There is one question
• Hay preguntas = There are questions

Hay comes from the verb haber, but in this use it does not change for singular or plural. It stays hay in both cases.

Because Spanish uses haber to express existence: there is / there are.

So:

• Hay preguntas = There are questions

You would not use estar or ser for that basic idea of existence.

Compare:

• Hay preguntas = Questions exist / There are questions
• Las preguntas están aquí = The questions are here
• Esas son preguntas difíciles = Those are difficult questions

Because Spanish often leaves out the article when talking about an indefinite plural in a general sense.

So hay preguntas means there are questions or there are some questions.

If you said hay unas preguntas, it would sound more like there are some questions, with a little more emphasis on some. Both are possible, but hay preguntas is very natural and neutral.

Yes, it sounds fairly formal, or at least neutral-to-formal, especially because of En lo que respecta a.

A more everyday version might be:

• Sobre la legalización, hay preguntas.
• En cuanto a la legalización, hay preguntas.
• Con respecto a la legalización, hay preguntas.

The original sentence is not strange, but it is more likely in written language, news, discussion, or formal speech than in very casual conversation.

Yes, Spanish is flexible.

These are all possible:

• En lo que respecta a la legalización, hay preguntas.
• Hay preguntas en lo que respecta a la legalización.

The first version is better if you want to introduce the topic first. That is why it sounds more natural in many contexts.

Because the opening phrase En lo que respecta a la legalización is an introductory topic phrase. The comma separates that introductory part from the main clause:

• En lo que respecta a la legalización = topic/frame
• hay preguntas = main statement

In English, we often do the same: As regards legalization, there are questions.

Yes. That is one of the most common alternatives.

• En lo que respecta a la legalización, hay preguntas.
• En cuanto a la legalización, hay preguntas.

En cuanto a is very common and usually sounds a bit more direct and less heavy. For many learners, it is also easier to use in everyday Spanish.

They are not the same.

• legalización = the act or process of making something legal
• legalidad = legality, the state of being legal

So in this sentence, la legalización refers to the topic of legalizing something, not the general concept of legality.

For example:

• La legalización del proceso = the legalization of the process
• La legalidad del proceso = the legality of the process