Postgresql cannot be sorted in Korean order.

SELECT * FROM table_name ORDER BY title but the title cannot be sorted in Korean order and can be sorted as it pleases. < may appear before < and it looks random.

(1) SELECT* FROM table_name ORDER BY title collate "C" works well, but what is collate "C"?

(2) Postgresql installed on a Mac can be sorted well without color "C" and cannot be sorted only on postgresql installed on Linux. Did I do something wrong when I set up the DB?