Why say "Hello"?

[Moros]

Hmm heil also exist in dutch but then it means something along the lines of something that saves something/somebody. (Can't find the proper English word.)

[L'Impresario]

Dutch is a germanic language, what did you expect ;)
If you mean something close to "saviour", then it's due to the Old Norse helge (sacred) branch of the IE root kailo~, which lead to halig, hailig, heilig etc.