... ok, I see that the answer is yes, according to the commit comment for eccfef8:
Currently, ICU-provided collations can only be explicitly named collations. The global database locales are still always libc-provided. I got there the long way, by first wondering how to tell whether a datcollate or datctype string was intended for libc or ICU, and then reading pg_perm_setlocale, and then combing through the docs at CREATE DATABASE and createdb and initdb and Collation Support and pg_database and the release notes for 10, sure that I would find the answer staring at me in one of those places once I knew I was asking. Next question: the "currently" in that comment suggests that could change, but is there any present intention to change it, or is this likely to just be the way it is for the foreseeable future? Regards, -Chap
