I woluld like to read the first unknown number of persons from France and process that data, and then continue with the unknown number of germans and process that, and so on.

create or replace
  procedure process_persons(
                            p_german number,
                            p_french number,
                            p_english number
                           )
    is
      cursor v_cur
        is
          with t as (
                     select  ...,
                             row_number() over(partition by nationality order by 1) rn
                       from  persons
                       where nationality in ('german','french','english')
                    )
          select  *
            from  t
            where (nationality = 'german' and rn <= p_german)
               or (nationality = 'french' and rn <= p_french)
               or (nationality = 'english' and rn <= p_english)
            order by case nationality
                       when 'french' then 1
                       when 'german' then 2
                       else 3
                     end,
                     rn;
    begin
        for v_rec in v_cur loop
          do-processing
        end loop;
end;
/

Welcome to the forum.

With any SQL or PL/SQL question, please, Post a working Test case: create table and insert statements along with the result you want with these data then we will be able work with your table and data. Explain with words and sentences the rules that lead to this result.

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I don't know how to declare the new cursor. I want to get the variable Var1 into a vector for processing.

...
Hint: you have to use a parametrized cursor.
Read PL/SQL User's Guide and Reference, Chapter 6 Performing SQL Operations from PL/SQL, section Managing Cursors in PL/SQL

Regards
Michel

I want the values in column Var1 into a variable X.

If a certain nationality had eg 3 records then there should be the values X(1), X(2) and X(3) to process in different complicated ways. So I want to know that there is 3 to deal with. Then if the next nationality had 2 records then the values should be put into X(1) and X(2) and so on.

I must know how many X-values(Var1) there is to process(in complicated ways).

I'd say the main problem is you still haven't told us what difference the number of rows for a given nationality actual makes to what the code is supposed to do.

"You must declare an explicit cursor for queries that return more than one row.".

declare
  cursor c1 is select dname from dept;
begin
  for c1r in c1 loop
    ...
  end loop;
end;

begin
  for c1r in (select dname from dept) loop
    ... 
  end loop;
end;

"rec" is the loop variable just like I in FOR I in 1..10 LOOP". It is a record containing all columns of your loop query.
Please READ the link I pointed you to, it contains ALL information about cursor and cursor loop (for instance in the section "Querying Data with PL/SQL: Explicit Cursor FOR Loops").

Regards
Michel

So I tried with both DBMS_OUTPUT.PUT_LINE(X) and DBMS_OUTPUT.PUT_LINE(t.X) inside the loop.

I get t´he message "identifier 'X' must be declared".

DBMS_OUTPUT.PUT_LINE(rec.X)