One of the biggest problems facing English-speakers learning a feign language has nothing to do with the grammar or vocabulary of the language. It is the social problem of using the familiar or polite form of the personal pronoun. Spanish has the familiar tú and the formal Usted, from Vuestra merced (Your Worship) and takes a third person verb. It’s not always an easy choice. It seems that tú is gaining ground, at least in Spain. Latin America is a different matter; the builder who did some work on my home a few years ago was a perfectly friendly man but he was Argentinian and insisted on Usted. I deal with publishing and distribution companies where Usted seems to be the norm for email but tú is used on the phone. I have heard it said, though I have no evidence, that the Civil War led to a breakdown of formality on both sides and an increasing use of tú. Something similar happened I think, too, after the English Civil War, which led to the disappearance (almost) of thou. The King of Spain, however, has it easy. Everyone calls him Usted and he calls everyone tú.
To make life harder, it’s different in different languages. German for example is much more formal than Spanish. To celebrate Bastille Day the LA Times published an interesting infographic about the use of tu and vous in French. The image cannot be extracted but I attach a screenshot of a part (click to enlarge). The full thing is very well worth looking at here.