Try use single quotes:

create database 'localhost:milenio-central.fdb' user 'milenio' 
password 'secreto' page_size 16384 default character set utf8 collation 
unicode; 

>   Hi,
>
> In firebird 2.x you can specify some parameters when creating a
> database, i.e.:
>
>     create database "localhost:milenio-central.fdb" user "milenio"
> password "secreto" page_size 16384 default character set utf8 collation
> unicode;
>
> However in fb 3.0 I get this error:
>
>     Use CONNECT or CREATE DATABASE to specify a database
>     SQL> create database "localhost:milenio-central.fdb" user milenio
> password "secreto" page_size 16384 default character set utf8 collation
> unicode;
>     Statement failed, SQLSTATE = 42000
>     Dynamic SQL Error
>     -SQL error code = -104
>     -Token unknown - line 1, column 17
>     -"localhost:milenio-central.fdb"
>
> if I strip out the "character set" and "collation" parameters, then the
> order runs fine again, but ¿what are the allowed parameters for "create
> database" in fb 3.0? ¿and what are the alternatives for unsupported ones?
>
> Thanks!