[deepsun]

Typical example in some slavic languages: singular/plural versions of "you". In official speech one almost never says singular "you" even to a single person -- instead using honorific plural "you".

I wonder if it was probably the same in English, just at some point people became all too polite and stopped using "thou".

[bloak]

Yes. And some Quakers were offended by all this unnecessary politeness and continued to use "thou" for a couple of centuries. So English and French used plural "you" for politeness, and so did German at one point, but modern German uses "they" as a polite "you", and so does Italian, I think. So there was an international trend to avoid singular "you" when being polite. But recently in Sweden (1960s/1970s) they've gone back to universal use of singular "you", which seems like a good thing to me, though it's presumably too late for English, despite the holdouts in Yorkshire.

[Tor3]

In Norway the switch happened almost overnight, approximately 1980. Good riddance, the plural polite forms didn't exist in my dialect anyway and it always sounded extremely cringy when somebody tried to use those forms in dialects which didn't have them.

I always say that it's not the words you use which matters for politeness, it's how you say them.

[inkyoto]

> […] In official speech one almost never says singular "you" […]

With a notable exception being addressing the sovereign (king/queen/tsar/etc) where the singular «you», «thou» and similar were used, in all languages. The sovereign was seen as a direct peer, the ultimate protector of the people and the last instance of appeal, and the connection was also perceived as deeply intimate.

The practice fell out of favour in England (I'm not sure when exactly but probably with the transition to the constitutional monarchy), although it lived on elsewhere in mainland Europe until the demise of all major monarchies.

[deepsun]

That probably stems from making people believe that sovereign is a semi-god, God's appointee. In religion, God was always addressed intimately, same when God addressed someone.