The following bug has been logged on the website:
Bug reference: 14778
Logged by: Glenn Burkhardt
Email address: glenn(dot)burkhardt(at)utas(dot)utc(dot)com
PostgreSQL version: 9.6.3
Operating system: Windows 10
Description:
For an unattended install with options "--mode unattended --locale en-US",
the installation fails claiming that no such locale exists. However,
--locale "English, United States" works. The standard Microsoft designation
of "en-US" is not recognized.