Modern German has separate formal and informal pronouns ("du bist" vs. "Sie sind") and verbs. English used to have them too ("thou art"/"you are"). Even though people assume "thou" is more formal, it's actually the informal/intimate version.
https://en.wikipedia.org/wiki/Thou
Apparently we (~Angles/Saxons) also used to have a separate tense for "a group of exactly two of you" and words like "both" (vs all) and "either" (vs any) are residual traces of this.
