I'm maybe anticipating but I saw that तू is mentioned as informal / intimate second-person singular. I'm used to tu / vous, du / Sie, tu / Vd. A binary informal / polite form to address one person. In Hindi, I think you have 3 forms. Intimate / informal / polite. Is तू safe to use with friends, younger people etc ? I don't want to use the "intimate" instead of the informal.
Correct , but tum shall be used even when speaking to children because it shows our humbleness towards them , we avoid speaking 'tu' to children , in hindi 'tu' is only used when someone is your close friend and both of you are of "same age".if i want to ask a child to come near me i will say- Tum idhar aao. But if im asking my best friend i will say- Tu idhar aa.
We use tu plus hain when the subject is very close to us , like u can say - tu pani piti(female)hai. To your best /close friend (girl), Tu pani pita(male)hai.to your close friend or younger brother, etc...........but even if the person is younger than/close to you you must say Tum Pani piti ho , which signifies how elegantly/humbly (adab-humble , adab se- humbly)you are communicating with your close ones too.