If someone simply feels like greeting you, they can. Hello is a greeting that people constantly say to each other.
In Sallan, you can say "Kalia" to greet someone with hello.
I say "Hello."
say hello
kitty says hello
In Tlingit, you would say "ḵwáanáx̱" to greet someone with hello.
when someone says hello you also say HELLO, hahaha der!!
You don't need to say hello, its just a polite way of greeting someone.
In Sudan, you can say "Marhaban" to greet someone, which means hello.
In Burundi, you can say "Amagara" to greet someone, which means hello.
In Waale, you can say "kɛ̀rè" to greet someone, which translates to "hello" in English.
In Abenaki, you can say "Aaniin" to greet someone, which means "hello" in the language.
In K'iche', you can say "qanjob'al" to greet someone with a simple "hello."