it says "el abuelo" in Spanish, why shouldn't that be translated as "the grandfather" instead of just "grandfather", including the article?
My understanding is that "el abuelo" often appears in places where we would say "my grandfather" (from the point of view of the speaker) or "his/her/our/their/your grandfather" if the subject of the sentence is some other person. It's sort of "the grandfather in question." Is that right?
What about "the grandpa" as in "the old man"? Is that considered unnatural English?
Yea, usually you'll never hear "the grandpa" in English, unless someone is talking about a different family in the third person, and even then it would usually be, "his grandfather" or "their grandfather" The only example I can think of for using "the grandfather" is a little dark, like in a crime tv show where the detectives are talking about a crime scene and say something like "The grandfather wasn't home when the incident took place."
This is the second place I've found where "at times" (perfectly good English phrase) is rejected for "a veces." Yes, Duo wants "sometimes" to be understood, but this should be accepted as well!