in which languages it is normal to address strangers as relatives?
For examples, in Russian it is rather normal for kids to call an adult man as "дядя" (uncle) and an adult woman as "тетя" (aunt).
IT is typical not only for kids, even adult address strangers as relatives.
If a stranger man is very old, older then 50, then people address him "дедушка" (grandpa) Very old females, older then 50 are addressed as "бабушка" (grandma)
It is absolutely normal to address a man 20 year older then you as "отец" (father) and female as "мать"(mother)
On Moscow streets older people address strangers as "сынок" (son) "дочка" (daughter) "внучок" (grandson) "внучка" (granddaughter)
Men of the same age address each other as "брат" "браток" "братишка" "братуха" "брателло" (brother)
This address was typical for criminal and military people before, but now it is widespread. Last time I visited Moscow I was addressed as "bratuha" by a receptionist in a four star hotel
I assume that it might be common for Indian people. When I visit my Indian friend, his children great me as "hello, uncle" but I am not a brother of his wife.