too many years of knowing which variables/array are available on an admin area page... 😉
out of the box, the stats array wouldn't contain those values about todo items...
you would need a simple hook to query the table to get the value - i've PM'd you a basic hook to do that, and it will give you a {$todostats} variable which you can use in the admin area template to show how many to do items there are that are not completed... as written, it gets the total for everyone, to get a total for the current logged in admin, you can just uncomment the line in the hook that i've commented out.
and then with regards to the language files, it's just a case of working your way through english.php (or your own language) to see if an appropriate string already exists for your need - if not, either use a Language Overrides or just hardcode it in the template.