My brothers name is [name_m]Lukas[/name_m] and my mother always calls him [name_m]Luke[/name_m] but the rest of the family and friends call him [name_m]Luki[/name_m] (in [name_m]German[/name_m] pronounced Lukee).
I guess it always depends on the country you live in. In [name_f]Austria[/name_f] probably everybody would assume that [name_m]Luke[/name_m] is short for [name_m]Lukas[/name_m]/[name_m]Lucas[/name_m] while I think in the US [name_m]Luke[/name_m] is more commonly known as a full name instead of just a nickname.
I agree. If I knew the parents well enough, I might ask if [name_m]Luke[/name_m] was short for [name_m]Lucas[/name_m] but I wouldn’t just assume it.
I have a cousin named [name_m]Jake[/name_m] and people sometimes assume he is a [name_m]Jacob[/name_m] which he isnt, but I think [name_m]Luke[/name_m] is a more widely acceptable standalone first name