Earlier quoted context omitted.
By definition there is no legal middle names here in Finland (all of the 1 to 4 names given to you are called "first name" in the law). And thus all of your names will be in the passport too. Filling some foreign (or poorly done/ported local) it system forms can be bit of a guess work. Also as a bonus space " " is a legal character in a name. Both "Jukka Pekka" and "Jukka-Pekka" are valid names (also you could have 2…
> "Jukka Pekka" [...] also you could have 2 names "Jukka" and "Pekka" How is that distinguished in legal documents/while registering the name/...?
As for how to register such a name correctly for a baby I have no clue. Also you don't have to give the baby a name at birth (you have 60 days) but the national identification number is given to the baby at birth (it is just date of birth, sequence number and a checksum character). All I know is that I have a colleague which such a name and have seen people before with space instead of - on a 2 part name
edit: How we usually do forms for this stuff is just 2 fields. One for all of your first names and the second for your family name(s) (you can have multiple for example both of your parents or some foreign with de/von/etc). Validation is mostly "check that they are not empty"