Fix for the Monolingual problem
I've had this problem with Office 2008 since day 1 and there is a fix which always works for me (including the latest update). It needs a text editor and nerves of steel, but little else.
1: First of all, get the update from the Mactopia site at http://www.microsoft.com/mac/downloads.mspx - you'll need to root around for the actual update as the featured 'latest' update is for Office 2004. Well done Microsoft.
2: Open the DMG file and drag the installer file on to the Desktop.
3: Go to the Desktop, right-click the installer file and choose [Show Package Contents].
4: Navigate down to Update/Contents/Resources/ and open the file package_updatable in your favourite text editor. You may be prompted if you want to make the file editable, say Yes.
5: Find the line 'found_valid_version=False'
6: Change 'False' to 'True'
7: Delete all the text below that line as far as the line 'if not found_valid_version:' BUT DO NOT DELETE THIS LINE.
8: Save the file.
9: Rerun the installer.
But why the Microsoft Office installer is so shite? Sorry can't help you there.