In: /mod/scheduler/lang/en/scheduler.php...

The following strings are each defined twice. One instance of the duplicate instances should be removed:

$string['modulename'] = 'Scheduler';
$string['modulenameplural'] = 'Schedulers';

Suggestion to make "Force Overlap Help" text easier to understand:

$string['forcewhenoverlap_help']='
<h3>Enabling overlapping of session slots</h3>
<p>This allows you to create slots that conflicts with other slots.
In such a case, only "clean" slots will be added. Conflicting ones will be ignored.</p>

<p>If disabled, you will be asked to delete existing slots before the being able to
add new slots when overlaps are detected.</p>';