What are the grammatical features/peculiarities of formal/informal "you" in different languages?
In English, as far as I understand, "you" is etymologically the formal form of "you". There used to be the informal you (thou), but now it's archaic ("Whither goest thou?").
In English the singular "you" is used as the plural "you", meaning "you all". "You are going there" could mean both "You [my little baby son], are going there", "You [sir] are going there", "You [two] are going there".
In German, they have both "du" (informal singular you) and "Sie" (formal singular you). Gramatically "Sie" behaves as the plural "sie" ("you all guys"), in spelling they capitalize the "S" in formal singular "Sie".
In French they use "tu" (inf. sng. you) and "vous" (formal sng. you). The formal "vous" behaves as the plural "vous" (you all), the same as in German.
In Russian there's "ты" (inf. sng. you) and "вы" (formal sng. you). The formal "вы" behaves as the plural "вы" (you all). In some contexts it should be capitalized, but the verbs that refer to formal "вы" are the same as for the plural "вы".
So in this German, French and Russian are quite similar.
In spite of being closely related to French, Spanish is different. They have "tú" (inf. sng. you) and "usted" (formal sng. "you"). But the verbs that are used with "usted" are conjugated not the same way as the plural Spanish "you" (actually there are two plural Spanish "you's" - ustedes and vosotros)! They are conjugated as the third person, singular - "he/she". "Habla" could mean both "He/she speaks" and "You [sir] speak". First is seemed very weird to me, but now I'm used to it.
As far as I remember, the similar usage of the formal "you" is in Polish. But they use "pan" in this context which actually means "sir", so the indirect polite addressing "Sir wants something?" sounds, well, logical. I'm not very sure about Polish, however, as I never formally studied it, I just used to watch a lot of Polish TV :)
What about your language or any other language that you know?
What are the reasons of having two "you's"? When you want to be polite, you try to address a person INDIRECTLY, and that's why you use the plural or the third person form of the verb?
Thanks for the answers!