I noticed that after switching to a Finnish language file, I get problems in the printable version of the monthly calendar view. The problem is related to having the week start on monday, not sunday as is default.
The normal, actual calendar view is fine. So is the printable version of the weekly etc views. In the normal 30 day view, the leftmost column is monday and is correctly titled "monday". However, when I open the printable version of the 30 day view, the leftmost column is titled "sunday", then "monday, tuesday", etc. The events and actual data on the view is correct but the column titles are wrong, they do not reflect the fact that the week starts on monday.
I checked the language files and I could not find any place where I would have incorrect definitions of weekday names.