I have no idea if this problem is related to Ubuntu or Xfce, but as I've already written on the Ubuntu forums, I have a problem with getting Xfce to localize in Norwegian.
I've downloaded all packages with "nb-NO" in them and set "Norwegian" in "System -> Language". However, Xubuntu is still serving me English. Well, mostly. Some menu items are displayed in Norwegian (like "File" ("Fil") and "Help" ("Hjelp")), but most of the text in Xubuntu is still in English. I've installed the Norwegian language packages for Thunderbird and Firefox too, but both applications are completely English. I've even tried to download the Norwegian language Add-on, without success.
You might want to try xfce on gentoo. In gentoo you can set packages to compile with specific LINGUAS flags, and they generally pay more attention than with binary-based distributions such as Ubuntu.
Since my computer-illiterate mother is going to use this computer, I'd like to be able to use apt to keep Linux and all packages automatically up to date. If I compile stuff myself, I won't get that luxury, no -- not even in Gentoo?