The following lists provide the standard strings used by Pulse for the button text for the confirmation. If you want to change those, you can use the language customization of Moodle. This only changes the presentation of the button and has no functional impact. For further information refer to the official Moodle documentation.
Strings for not completed state button text
markcompletebtnstring_default: Mark as complete
markcompletebtnstring_custom1: Acknowledge
markcompletebtnstring_custom2: Confirm
markcompletebtnstring_custom3: Choose
markcompletebtnstring_custom4: Approve
Strings for completed state labels
markedcompletebtnstring_default: Self marked complete on {$a->date}
markedcompletebtnstring_custom1: Completion acknowledged on {$a->date}
markedcompletebtnstring_custom2: Completion confirmed on {$a->date}
markedcompletebtnstring_custom3: Completion chosen on {$a->date}
markedcompletebtnstring_custom4: Completion approved on {$a->date}