Welcome group email translation

Hi, I would like to know if there is a way to fully translate the "welcome email" that members of a Group get when they are added to that Group.

I realized that some of the text is customizable, e.g. I could translate the text after "Message From Administrator : -"

But I can't seem to find how/where to translate other sentences like: "ACCEPT THIS INVITATION" or "Your confirmation is needed for receiving emails addressed to"

Is a fully customizable welcome email possible?
Thanks,
Daniel.