You're correct - seems I missed copying the renamed action to the template...
Until a fixed version is available, just rename the current "Anzeigeoptionen\De-Mail" action into "Mehr\Als De-Mail versenden" and embed it as described in the documentation. The code behind is exactly the same. There is no additional form getting opened in Notes, instead, this action activates an additional subform in the Notes mail header. Renaming in 0.5 is more because of mirroring the iNotes approach that flags an individual mails as a De-Mail vs. the 0.4 approach to enable/disable De-Mail for all mails.