You’re not using the new rule based mechanism, but the LanguageBasePlugin does.
It’s true that having an error in this internal plug-in, about something you’re not even using, is wrong. There is most likely a bug here.
However, using the rule based mechanism to create your task (which is one of the well documented things one can do using the current state of the rule based mechanism) might integrate better with internal plugins that already use it, and might be a viable work around the problem.
For the rest, I let the experts intervene.