[CentOS] Locales and filenames

I have a file which contains non-ASCII characters (umlauts, accented  
characters, etc.) both in its filename as well as its content.  The  
only way I have been able to see these characters is inside vim,  
where they are displayed correctly no matter what I have LANG set  
to.  My default LANG is en_US.utf8, but I have tried de_DE.utf8,  
de_DE.iso88591, and various others.  In the output of a simple ls,  
the characters are shown as either a simple "?" or a "?" in a box  
depending on what I have LANG set to, and the same is true if I use  
cat to display the contents.  I have tried this both in an xterm as  
well as a gnome-terminal window on a CentOS 5.3 system.

I am taking stabs in the dark here as I've never had to deal with  
LANG and locales before.  Am I missing something obvious or is there  
more to it than simply setting LANG.  Since I can see the characters  
correctly in vim, I'm sure it's not a font issue.  I just want to be  
able to display these characters correctly with simple Linux commands  
like ls and cat.

Thanks,
Alfred