All that being said, that input label has a ‘t’ in front which indicates it’s translatable through the Dashboard->Multilingual . I have never translated a site so I’m not the expert on this.
@mhawke You’re correct in that you can translate the whole site,
Have a look here.
I recently created a dutch and french version from an english site using the copy language amd the translation tools in concrete. It was very good and fairly easy to setup. We then hide the UK version.
I’m afraid I have no clue. That label is a concatenation of HTML and attribute values so finding where that takes place in the core is difficult for an amateur like me. Searching the core for the word ‘Required’ results is a bizzilion hits. I think you’re getting ‘in the weeds’ here trying to semi-translate only certain things but not everything. Others with more experience in the translation mechanism will have to chime in here.