I just noticed that in lib/outputrenderers.php the standard_footer_html uses the hard coded words ... This page is: rather than...

get_string('thispageis', 'admin');

in this section...

if (!empty($CFG->debugpageinfo)) {

            $output .= '<div class="performanceinfo pageinfo">This page is: ' . $this->page->debug_summary() . '</div>';

        }

I know this is debugging which may not necessitate translations. Even so I thought I would flag this just the same.