What is a Collation, and Why is My Data Corrupt?

The GNU C Library (glibc) version 2.28 entered the world on August 1st, 2018 and Postgres hasn't been the same since. Among its many changes was a massive update to locale collation data, bringing it in line with the 2016 Edition 4 release of the ISO 14651 standard and Unicode 9.0.0. This was not a subtle tweak. It was the culmination of roughly 18 years of accumulated locale modifications, all merged in a single release.