When the multilang filter is enabled (with "filter all string"=true), language filtering works with some quiz question types but not with all. In my tests with Moodle 1.6.4 at least "multiple choice"-type questions works well, but "matching"-type questions have some nasty issues. The problem with "matching"-type questions is that the question text (the text which asks the student to do something) itself gets filtered but the matches are not processed by the multilang filter: the matches show all the <span>-tagged language alternatives instead of just showing one language at a time. If you take a look at the attachment, you can see "SUOMEA"-text in the dropdown menu (shoudn't appear in the menu).
I browsed thru the forums and found some messages with very similar problems. Some of the issues were published in September, 2004, but at least to me some of the issues seem to exist still in the newest 1.6.4 code. See: