Du0lingo most often cross-genders the voices and sentences. It may be for pedagocial reasons, to make us really check what is being said rather than automatically react to the gender of the speaker. But considering the company's heavy LGBTP agenda, it may be (or also be) for political reasons.
I am from Ukraine, and here if one calls their relatives with the polite pronoun it means they are not close and the parents or grandparents have a strong traditional and hierarchical views. It seems like a horrible relationship to me. My grandmother is my friend, and if I ever wanted to insult her, I would call her the formal word.
Sehr interessant! I'm old-school: I like the formal, polite, pronouns. One of my pet peeves is people with whom I am only vaguely acquainted assuming, or presuming, to address me by my first name, as though we were on intimate terms.
I'm also very fond of the German formal, oral grammatical structure: what it that, is that the Future Perfect?
But this discussion partially explains why Duo insists on using that very rude sentence, "Du bist toll!" I might say that to my Teddy Bear, but certainly not to someone I've just met, nor even to someone I know well enough to "Du". I have more respect for my loves ones than to call them insane; and, to call a new or casual acquaintance "insane" is, well, bad manners.
I was going to ask something related to this: is Enkel (grandchild/grandson) similar to the Spanish niño (child/boy)? As niña specifically refers to "girl" but niño can be either "child"/"boy" depending on context.
My conclusion (tl;dr): Enkel is "grandchild"/"grandson" while Enkelin is only used for "granddaughter" (correct me if I'm wrong!)