[To clarify, 'show' icons use the 'hide' string]
Applies to course formats: topics, study [OU] (commented code), and weeks, weekcss (not used by OU at present). Applies to OU and main Moodle CVS (MOODLE_16_STABLE branch, head).
Concerns the 'title' on the link, and 'alt' text on the image.
In each case both strings are created, but the 'show' one is not used:
$strweekhide = get_string('weekhide', '', $strstudents);
$strweekshow = get_string('weekshow', '', $strstudents);