Translation:When are you going to ask them about their vacation?
I wonder if the usage of las here is similar to the usage described in the lightbulb in the Routines 3 section. https://www.duolingo.com/skill/es/Routines-3/tips. DL say's it's specific to body parts, but my wife, a native spanish speaker, says that 'las' sounds correct to her. She can't explain why though.
You are not wrong, Eliza. This is simply a plural noun (always). Alec, you might compare las vacaciones to the way we use "pants" in English. Yes, we refer to "a pair of pants", but we also just say "I need to put on pants" or "some pants", etc. It just isn't as obvious to us because the direct article "the" doesn't change with plural nouns in English.
You're being overly literal and expecting on-line translators to replicate DL answers out of context.
Compare to the English sentence: "When are you going to tell us about vacation?" Any fluent English speaker would know the question concerned either (a) a recent vacation, or (b) an upcoming vacation. Yes, of course, one could ask about "your vacation", but "your" isn't necessary to understand the question.
You will find lots of examples in Spanish where a simple direct article is used in place of a possessive pronoun. Ex. Tengo duele en la cabeza. "I have a headache." Spanish doesn't usually say "in my head"; "in the head" suffices. (This isn't a perfect analogy, just another example of where the word-for-word translation you want isn't necessary.)
In my version of DL, this question provided a list of words from which to select the correct answer. However, the word "them" was not one of the provided words. So, I said "when are you going to ask about their vacation." For this I was marked wrong. How can I select a word which is not listed as an option? Obviously, I have reported this but that won't give be back the health star DL has stolen. I have lost many health points because of keyboard errors and obvious typos but this takes the cake.