Your sentences from the movie are examples of what is called "redundancia pronominal" or "reduplicación/doblado de clíticos" ("clitic doubling"): there is an object in the canonical position ("a su novia" in your case) and also a clitic pronoun ("le" in your case) with the same syntactic function. As explained in the Enciclopedia de lingüística hispánica, by several authors, it's a phenomenon that singles out Spanish with respect to other Romance languages (but this is not exclusive of Spanish: this also happens in Catalan with a lower extent).
In your case, what is duplicated is the indirect object ("le" and "al estúpido"). This book explains that there are situations in which such indirect object duplication is mandatory and others in which it is not, although the option with duplication is by far the preferred one.
The duplication is mandatory when the object (direct or indirect) in the canonical position is constructed with a pronoun (with some exceptions). For instance:
- María me llamó a mi.
- Yo le di el regalo a ella.
You cannot say "María llamó a mi" or "Yo di el regalo a ella". In the same way, you can say "preguntémosle a él” or "vamos a preguntarle a él", but not "preguntemos a él” or "vamos a preguntar a él".
The exceptions to this rule are the pronouns "usted" and neutral "ello" which do not require duplication, as in these examples:
- Para servir a usted.
- Es cuanto tenemos que decir a usted, señor presidente. (CREA, España, 1996)
- La EMT agradece a usted la utilización de sus autobuses.
- Dedicaré a ello el siguiente capítulo.
In other cases, duplication of indirect object is mandatory or not depending on its semantic role: it's (relatively) optional when this object express the target or the recipient, as in this example,
- María le entregó el paquete a su dueño / María entregó el paquete a su dueño
or these other examples from the book Gramática descriptiva de la lengua española, by several authors:
- Le dijeron a Juan que viniera / Dijeron a Juan que viniera,
- Le dieron el premio al escritor / Dieron el premio al escritor.
But duplication is mandatory when indirect object has other semantical roles: what are called experiential ("experimentantes", which means that the role of the indirect object is to convey who is experiencing or feeling what is being expressed by the verb)
- Nunca le gustó realmente el cine a María (you cannot say "Nunca gustó realmente el cine a María"),
- María le hizo los deberes al niño (you cannot say "María hizo los deberes al niño"),
- Le preparó un brebaje al enfermo (you cannot say "Preparó un brebaje al enfermo")
and (inalienable) possessor datives
- Aquí le rompieron la pierna a Juan (you cannot say "Aquí rompieron la pierna a Juan"),
- Le cortaron las uñas al niño (you cannot say "Cortaron las uñas al niño"),
- Le duele la pierna a Pedro (you cannot say "Duele la pierna a Pedro").
Note that, in your sentences from the movie, "el estúpido" has the role of recipient or target of the verb "preguntar", so it corresponds to the case in which duplication is (relatively) optional: as in the examples "Dieron el premio al escritor" and "Dijeron a Juan que viniera", one can also say "Preguntemos al estúpido".
But, in this other sentence from your question
- Mi idea le pareció al profesor la más interesante,
"el profesor" of the indirect object is the person who is feeling what is expressed by "parecer la más interesante", so it corresponds to one of the cases in which duplication is required. That is, in this instance, you can not say "Mi idea pareció al profesor la más interesante" without the clitic "le".
And, as stated in the comment by OnlyThenDidIReckonMyCurse, you can say both
- Le traigo unos libros a mi hermana / Traigo unos libros a mi hermana,
but not "Le traigo unos libros a la escuela" because "a la escuela" is not an indirect object, but a place complement, so one cannot use a dative pronoun in this sentence.
Note also that what's being said in some answers to this other question, namely something like "I'm a native speaker and the version with the clitic pronoun le sounds better to me", completely agrees to what is explained in the above cited books in reference to the case in which the presence of the clitic pronoun is (relatively) optional:
la opción del doblado es, con mucho, la preferida
and Gramática descriptiva de la lengua española adds to this statement
Véanse Silva-Corvalán 1981 para el español chileno; Bentivoglio 1978 para el Caribe y Barrenechea y Orecchia 1977 para el bonaerense.
The book Complementos argumentales del verbo: directo, indirecto, suplemento y agente by José-Álvaro Porto Dapena, gives also an example which is similar to your sentences in the sense that an indirect object is present but there is no need of clitic pronoun. In this case, it's written without the clitic pronoun:
- Nicolás regaló una moto a su hijo
(you may also perfectly say "Nicolás le regaló una moto a su hijo").
In addition, this book provides some instances of constructions that also require the presence of a clitic pronoun (this happens also in other Romance languages) without a duplication of the indirect object, namely, what are called "etic dative" ("dativo ético"), in which the presence of the clitic pronoun adds to the sentence an intensive value, expressing a greater participation of the subject in the action expressed by the verb,
- Se bebieron toda la cerveza
and "possessive dative" ("dativo posesivo"), in which the clitic pronoun adds the semantical role of possession to other noun phrase present in the sentence:
- Le llevaron el equipaje a la estación,
- Nos ocuparon los asientos.
These are examples of a complete different phenomenon because, as you can see, there is no duplication of the indirect object in the above sentences; but it is a peculiar use of dative clitics which can give also rise to wondering about the role of such pronouns.
Notice that I've not included in the above explanation what are called "left dislocation" ("dislocación a la izquierda", for instance, "A Juan le han dado un premio") and "right dislocation" ("dislocación a la derecha", for example, "No le dieron el premio, a Juan"), which are different phenomena also requiring the presence of clitic pronouns that duplicate an indirect object and that are not characteristic of Spanish language, but are also present in other Romance languages. So, let's explain them.
Dislocations are constructions typical of oral speech, although one can also find them in written texts which do not have a high degree of formality.
A left dislocation of an object consists of a direct or indirect object (more generally, a noun phrase which acts as complement of the verb) which is written at the beginning of a sentence and then repeated in the sentence in the form of a clitic pronoun. For instance, in this example from Enciclopedia de lingüística hispánica
what is dislocated to the left is the direct object "Ese libro": notice how such direct object is again present in the sentence by means of the pronoun "lo". An example in which the indirect object is dislocated to the left may be
- A Juan le dieron un premio.
As explained in detail in Enciclopedia de lingüística hispánica, in Spanish, as in other Romance languages, we tend to transmit information in such a way that the news comes after the known things. For this reason, one frequently needs to alter the order subject-verb-complements of the sentence components, which is the one that is felt as neutral, specially in oral speech. Left dislocations is one of the resources the language has to achieve this. So, for instance, one can say to some friends
- A Juan le dieron un premio
if all of them know who is Juan and the news one wants to transmit is the fact that they have been awarded a prize. But if everyone knows that a prize has been awarded and the news is who is the winner, I would said instead
- Dieron el premio a Juan Goytisolo,
which in oral speech is more likely to be expressed as
- Le dieron el premio a Juan Goytisolo.
Notice that left dislocations of an object (direct or indirect) require object duplication by means of a clitic pronoun. In a certain sense, you can think about this as if you have decided to put the object "out of the sentence". But, once you make such decision, you must add to the sentence a clitic that has the same syntactic role of such object, otherwise it would lack of something.
An exception to this rule explained in Enciclopedia de lingüística hispánica is when the dislocated object is an undefined noun phrase. Since Spanish lacks of undefined clitic pronouns, in this case there is not object duplication by means of a clitic, as it happens in this sentence:
- Carpetas rojas, yo no he visto.
As explained in Enciclopedia de lingüística hispánica, in Spanish right dislocations are much less frequent than left dislocations, but are quite used in Italian and Catalan. In "Hablado/Parlato: aspectos
lingüísticos y discursivos de la
comunicación oral", an interesting paper by Félix San Vicente (University of Bologna) which compares these and other oral constructions in Spanish and Italian, it is even stated that right dislocations in Spanish may sometimes seem somewhat unnatural. When you make a right dislocation of an object (direct or indirect), first of all you produce a complete sentence that contains a direct or indirect object pronoun and then you decide not to finish the sentence there, but to add the direct or the indirect objrct of the sentence for further clarification. An example of right dislocation of the direct object from Enciclopedia de lingüística hispánica is this one:
- La dará la doctora Pujol, la conferencia plenaria.
And here is an example of right dislocation of the indirect object from the above cited paper by San Vicente:
- No, no le han dado el alta, a Juan.
Note that in these constructions there is a direct or indirect object in the form of a clitic pronoun and then it's duplicated by expliciting such object. As explained by San Vicente in their paper, a typical situation in which right dislocation is used is a conversation in which
el hablante, debido a un gesto o movimiento por parte de su interlocutor, interpreta que la comunicación no se ha percibido del modo adecuado (por haber supuesto un conocimiento compartido, o
bien por descuido u olvido) y recupera la información que se suponía elidida
That is, the speaker, due to a gesture or movement of their interlocutor, interprets that the communication has not been perceived in the appropriate way (because they have supposed a shared knowledge or
either by inattention or oversight) and retrieves the information that was supposed to be elided.