In Persian if someone expects to be spoken with formally, they have to speak formally themselves. So when you speak formally you're kinda bringing both parties up. You can even flirt by speaking formally.
The V is gradually being dropped in Spain and in the last few decades the process seems to have accelerated, though, definitely it seems faster than in French (although I don't know that much about French). I don't think my 4-year-old son will have much use for the V in his life. And like your parent comment, I also think that's probably for the best in our case, although it does sound like it's probably different in Persian.
I own a Spanish textbook printed (in English) in 1958 that says about «usted»: ‘It is the universal respectful address of society, and the only one the foreigner is ever likely to employ or hear addressed to him, unless he marries a native or forms intimate friendships.’ How times have changed!
vos is not really formal in Argentinian Spanish, although it does share an etymologocal root with vuestro merced/Usted.
Argentinian Spanish is itself pretty different from other Latin American dialects, but in general vos is used interchangeably with tú, to the point where the accusative form of "vos" is also te - ie, "Vos te levantás" instead of "tú te levantas" (note the location of the accents in each example).
The connotations of formality (or lack thereof) are subtle and vary much more widely than you might imagine - far more than the comment limit on HN would permit - but by and large it's better to think of vos as the informal pronoun, and the only question is whether it's used alongside tú, in place of it, or in some weird combination that has its own subtle connotations.
E.g.,
Formal polite: military, business email, public announcement
Formal non-polite: textbooks, novels
Informal polite: kids' books, between coworkers, between customer and clerk
Informal non-polite: siblings, childhood friends, mom to kids
Sorry for all the questions. I just found it fascinating.
But I could relate it, as it was a "chic" thing to do in my parts too back in the day (until around the 1970s), for upper class folks (using the polite forms of address, and so on).
A good analogy in English terms might be the flirting with all the speaking formalities in period movies live "Room with a view" or "Pride and Prejudice".
On the other hand you can't dirty talk with a straight face in Persian, since nobody has ever heard or read about it, it sounds super funny.
I recall the One-Thousand-and-One Nights being quite bawdy (talking about lusting after well-endowed servants, IIRC); maybe that's not authentic Persian literature though?
Maybe I misunderstood "nobody has ever read or heard about it"?
Can you help me better understand your comment, thanks.
New Persian literature starts around Rudaki (9th century). Since Islam made sex and showing affection taboo, the tiny fraction of explicit erotica are not studied/known by the general public. Because of the taboo, majority of Persians have not ever heard their parents speak affectionately. And when we study affectionate literature in school the teachers tell us it's about the love for God, and the exams will question us about such love.