Locale X is a major new version. For all of the new features in Locale X, please see the Locale X release announcement. 10.1.139 is a minor update with the following improvements:

Improved reliability during application startup, especially on Samsung devices
Improved reliability connecting to the Google Play store, especially when refreshing subscription changes
Emails generated by the Contact Support screen now include subscription information, making it faster for us to provide support
Improved compatibility with Android 14

Note: As a normal part of our release process to ensure high quality, updates to Locale X roll out in phases over a multi-week period. It may take some time before a specific update becomes visible to you.