In Moodle 2.2.2+ (Build: 20120427), the course completion report strings
are used for both activity completion status and course completion status. That is ok for English language where the terms are the same, however that may not hold true for other languages.
For example in Italian language a "course" is "completato/non completato" while an activity is "completata/non completata". Using the same term does not allow a correct translation for those languages.