Robot Framework 6.0 is a new major release that starts Robot Framework's localization efforts. In addition to that, it contains several nice enhancements related to, for example, automatic argument conversion and using embedded arguments. Initially it had version 5.1 and was considered a feature release, but it grow so big that we decided to call it a major release instead.
For more details see the [full release notes](https://github.com/robotframework/robotframework/blob/master/doc/releasenotes/rf-6.0.rst).