Content translation version 2 is a new version of Content translation that is aimed at providing a more solid and powerful editing experience, and better supporting the needs of newcomers. Version 2 uses the editing surface and many of the tools provided by Visual Editor.
Version 2 is now the default version. Initially it was provided as an opt-in feature.
For more details about the progress of version 2, you can check the project page. There you'll find status updates of the improvements made to the new version every week.