Cyrillic in PostgreSQL regex – Database Administrators Stack Exchange

I have difficulties with inserting cyrillic names into PostgreSQL database. It would be great if I could use locale in pgAdmin. Precisely speaking I am trying to set regex check for inserting cities names.

ALTER TABLE cities DROP CONSTRAINT cities_city_name_check;
ALTER TABLE cities ADD CONSTRAINT cities_city_name_check CHECK (city_name SIMILAR TO '[\u0400-\u042F]{1}[\u0400-\u04FF\'- ]{2,}');

Query returns syntax error.
SQL state: 42601
Character: 123