No way to translate the emails content.

AlGab → changed the visibility of the branch 1.0.x to hidden.

It doesn't seem like a good idea to duplicate all schema of the email handler this handler extends. That way, any time something changes in the parent handler, this handler will need to be manually updated as well.

Did you test version 1.0.0-beta2 or higher? Because since that version the config schema is set in config/schema/webform_email_confirmation_link.plugin.handler.schema.yml and altered in the webform_email_confirmation_link_config_schema_info_alter() hook. If something is not working as expected, those files should be fixed.