Hierarchical query from two tables
Assuming kgs_id is the primary key of both tables (which is a little strange), join the tables before doing the connect by:

select kgs_code, kgs_name
from (select * from dic_kgs join dic_kgs_strings using(kgs_id))
start with kgs_parent_id is null
connect by kgs_parent_id = prior kgs_id; 


alternatively look up kgs_name after the connect by (this approach can be helpful in more complicated situations such as if not all records in dic_kgs have a corresponding record in dic_kgs_strings):

select kgs_code, ( select kgs_name 
                   from dic_kgs_strings 
                   where kgs_id=kgs_code.kgs_id ) as kgs_name
from dic_kgs
start with kgs_parent_id is null
connect by kgs_parent_id = prior kgs_id;