Rossie, print_password_policy() is a typical example how strings should not be handled. We must not compose sentences in Moodle PHP code even they look like a proper English sentence. The form may not fit other languages. Unfortunately, our current get_string() implementation still lacks a possibility to define complex language logic like this case (it est a list of password policy rules).
I am going to remove the ", and" at the end at least and will add this example as an use case for the new get_string() features.