"You are talking to them."
Translation:Tu leur parles.
Whenever a pronoun is preceded by the word "to" in a sentence, we understand it to represent an indirect object. In the sentence "You are talking to them," we can infer the word "them" represents an indirect object because the word "to" can be found right before it. (In general, note that other words which indicate an indirect object in the place of "to" are "for" and "at.")
Contrast this with direct objects. If a pronoun appears directly after a verb, it represents a direct object. For example, take the sentence "I am carrying him." Here, "him" represents a direct object as the pronoun appears straight after the verb. There's no use for the word "to" here.
Depending on whether an object pronoun in a sentence represents a direct or indirect object, "them" is translated as "les" or "leur" respectively. (The only other object pronoun that has distinct translations for direct vs. indirect usage is "him." In this case, the appropriate translations are "le" and "lui" respectively.)
So again, the sentence we have here is "You are talking to them." The presence of "to" indicates "them" as representing an indirect object, hence we translate it as "leur."
Note that there are tricks with this rule. For instance, "I am reading him a book" is spoken in French as "Je lui lis un livre." Why have we used "lui" here (the translation for an indirect object) when the absence of the word "to" in this sentence supposedly suggests "him" represents a direct object? Don't be fooled: the phrase "I am reading him/her/them [a book, a newspaper, an article, etc.]" is a colloquial construction in English. If we were to be formal, we would say "I am reading a book TO him," hence revealing the true nature of the pronoun "him" as representing an indirect object in this context.
A rule of thumb to help you avoid potential slip-ups like the one above: look closely at the verb in the sentence. If it is a transitive verb, i.e. a verb that must be accompanied by an object, any pronoun used in conjunction must represent a direct object. If it is a verb that can be used with no further reference to an object, any pronoun used in conjunction must be an indirect object. (A word of caution: notice that this rule is useless in cases where either a direct or indirect object can, in theory, appear with a given verb (and offer different meanings), e.g. with the verb "give." But it still has its place, as I demonstrate below.)
Ex: "Love" is a transitive verb. The phrase "I love" or "they love" doesn't make much traditional sense without reference to an object that is the recipient of our affection. We always specify something receiving our affection when we use "love" as a verb, e.g. "I love you," or "they love it." Hence "you" and "it" must represent direct objects in this case.
Contrast with "speak." This verb has full meaning without an object being used; the sentence "I am speaking" makes perfect sense. But in the specific case that we are somehow connecting the verb to an object, we would use the word "to" for reference, e.g. "I am speaking to her." The fact that the reference of an object here is optional and presents very specific information tells us that "her" represents an indirect object in this sentence.
I have no idea if "leur" sees adoption as a singular gender-neutral pronoun in French as with "them" in English, but similar to its English counterpart, "leur" as a pronoun (not a possessive adjective) is already widely understood as plural. Assuming it does see use as singular, take it that "leur" does not vary as a pronoun. It just means "them" and context is used to determine whether it's intended as singular or plural, similar to English.
I used sitesurf's explanation that I noted: "aux = ...."a + les ( to them)... so I wrote: vous aux parlez you are talking to them and got it marked wrong. I almost feel I need to copy what the computer wants that I can continue with Duo... in another exercise, without understanding what I need to do... just to be able to continue the language tree.