Thanks German for raising this.
It is a known limitation of the current blocks management system. This "content" region is a custom region defined by the dashboard page via
$PAGE->blocks->add_region('content');
These custom regions do not have a human readable name string associated. Adding support for localising them would require some non-trivial development and refactoring. Please report that feature request into the tracker if you think it is worth it (I don't think it would get priority though, it is not an essential feature).