| This kind of thing is virtually universal in Europe, even in the unrelated languages Finnish, which uses second-person plural sinä, and Hungarian which uses maga with third person, and Basque, which uses plural zu as formal singular and has created a doubly-plural from zuek for the plural. I don't know when it began, though I am led to understand the first known occurrence of plural for singular is in Latin in the poetry of Catullus. English has actually lost the formal/familiar distinction by virtue of losing the old singular thou entirely.
The distinction is commonly called T/V by linguists (yes, that's what we have fun doing, we talk about T/V and if we're Latin-lovers we might even try it out) because of pairs like French tu ~ vous, and Russian ty ~ vy. However, note that Spanish plural vosotros, -as is the T (familiar) form, since the V (formal) is usted(es).
As well as the shift from singular to plural (and no I don't know why that should be honorific or polite), many European languages use roundabout third-person constructions, like the English "Does Modom wish to pay for Modom's hat now?" and "Your Majesty is like a stream of bat's piss". In Portuguese they say o senhor 'the gentleman', a senhora, and so on; in Romanian it's domneavoastra 'your lordship'; Spanish usted comes either from Arabic ustad 'master' or from vuestra merced 'your honour(?...roughly).
In Italian the noun for 'excellency' being feminine, the pronoun lei 'she' is also used for 'you' (singular).
In German they use Sie 'they', but I don't know why.
Elsewhere in the world you get somewhat similar-looking systems, but actually more complex. Both Japanese and Indonesian have several actual pronouns, or you can use titles such as sensei or Indonesian Bu 'Mother' (to an older woman), Tuan 'Lord', or you can use the names, as Tanaka-san or Abdul, with significant etiquette behind the choice. | 
