Update: Locale 6.4.0 has rolled out to 100% of users.

Locale® 6.4.0 is a unified update for Android 4.4 through Android 9 now beginning a phased rollout on Google Play. This means that Locale 6.4.0 will be available to 20% of users today and will scale up to 100% of users over the next couple of weeks. Because there are tens of thousands of different Android devices, phased rollouts help ensure that Locale upgrades work great for everyone.

Specific changes in Locale 6.4.0 include:

Minor bug fixes
Updated Android libraries, which contain a variety of bug fixes
Updated license agreement prompt screen
Internal database upgrades in preparation for the upcoming release of Locale X