Localization System not showing up in package manager

I read about the Localization System here:
https://docs.unity3d.com/Packages/com.unity.localization@0.5/manual/Installation.html

It seems pretty cool and I want to check it out for some future project. However when looking at my Package Manager with preview packages enabled I do not see the Localization System:

Does anyone else have this issue? Is the System called differently? Am I doing something wrong?

I am using Unity 2019.3.0.f3. I have added the new Input System (also in preview) through the package manager. So I don’t think this is an issue with the pm… or is it?

https://forum.unity.com/threads/release-announcements-and-notes.597262/

This package is currently in preview and not visible in the Package Manager. To install the package type in com.unity.localization under “Add package from git URL” in the Package Manager.

(Installation guide | Localization | 0.10.0-preview)

This package is currently in preview and not visible in the Package Manager

There is a “Show preview packages” option in the Package Manager.
If it doesn’t show the preview packages, what does it do?