ICU collations are prepopulated; see <https://www.postgresql.org/docs/devel/static/collation.html#....
Also, ICU collations are case sensitive, just like libc locales.
Also, ICU collations are case sensitive, just like libc locales.
Anyway, thanks a lot for this patch! It looks like it was a lot of work, and I'm very happy this made it into PostgreSQL 10.