This is related to the other language-related bugs, such as: #376858: Language file not found error although it's different enough to warrant a separate report.
When the String Overrides module is installed, even when Drupal hasn't been set to use a different language, Shadowbox looks for a language file named: modules/shadowbox/shadowbox/build/lang/shadowbox-xx.js. For those other language file issues the answer is to install the correct language file, but this case is different, as Shadowbox shouldn't be looking for a different language file at all.
Whether it's possible to fix this and which modules responsibility the bug is, I don't know. Perhaps the incompatibility should just be documented somewhere.
For reference: the workaround I used was to ln -s shadowbox-xx.js shadowbox-en.js when SSH'd into the server. Or, using an Ubuntu desktop, it's possible to right-click on the 'shadowbox-en.js' file and select Make link... and rename the created link to 'shadowbox-xx.js' then upload the link to the shadowbox/build/lang/ directory. Just copying the file would also work fine. :)
Comments
Comment #1
liam mcdermott commentedWhoops, selected the wrong version. :)
Comment #2
psynaptic commentedCommitted fix to DRUPAL-6--2 and DRUPAL-5--2:
http://drupal.org/cvs?commit=253756
http://drupal.org/cvs?commit=253758
Please test.