WinDjView Portable

This looks like a good candidate. I may look at it.

I haven't downloaded it, but a quick scan of the source code indicates that its profile path (as it calls it) can be overridden with the environment variable DJVU_CONFIG_DIR. (Reference: libdjvu/DjVuMessage.cpp, lines 141 and 272.

I may look at doing this one soon. In the mean time, if you want to you could try a basic thing by just creating a batch file (e.g. WinDjView.bat) with

set DJVU_CONFIG_DIR=%cd%\profile
WinDjView.exe

Where you create a "profile" directory inside your WinDjView directory. This is just if you're too impatient If not, just wait for me

Edit: note to self, will require default data, and uses environment variable LANGUAGE for the language setting.

I've just released WinDjView Portable 1.0.3 Development Test 1.

I have been using a portable version of STDUViewer.
It is freeware - not open source but has the advantage of opening up all of the following formats:

Tagged Image File Format
DjVu File Format
Portable Document Format
Text File Format

This program has been requested on this site previously but I'm not sure what happened about it.