Our user manual can be translated using Crowdin.
You need to request access to Crowdin on our developers mailing list. You will then be granted translator access on the platform.
Only the user manual for the current development version is being translated. When we publish a new stable version, we take a snapshot of this and publish it on the website.
In the meantime the pages you translate will be visible under https://docs.openrefine.org/next/ after a few days.