Today, only en_US.UTF-8 can be chosen for collate order which makes the database useless if you are storing any other language in the database. It is both easy to add and truly vital for the database to support more than just en_US.UTF-8 if you want the Managed PostgreSQL to be used by other people than U.S citizens.

Also this should of course be possible to set when the database is created in the UI.