The non-default section names of a course (in topic view) are not displayed correctly with multilang filter turned on. It shows all texts one after another.
Just add a format_string() to line 222 in /course/format/topics/format.php
echo $OUTPUT->heading(format_string($thissection->name), 3, 'sectionname');
Another fix regarding multilang in section names: If you edit a section/summary of a section, the title "Summary of..." is not displayed correctly. This can be fixed in line 69 of /course/editsection.php
$strsummaryof = get_string('summaryof', '', format_string("$sectionname"));
I updated this issue adding some screenshots. I think it's an important fix for multilingual moodle installations, because every student will see this bug in a course.