This site has a nice selection of British and American songs from WW1:

http://www.firstworldwar.com/audio/index.htm

with a bit of German and Italian material. But there were a lot of other nations involved, and that site doesn't even have French songs
(there are a few here: http://www.fncv.com/biblio/musiques/). Has anybody tried to put a wider range of stuff together on the web?

I know a bit about the Turkish songs of the period (mostly fatalistic gloom with no trace of jingoism) and I could probably find Armenian genocide songs quite easily (even more gloom). But there must have been songs from Russia, Hungary, Poland, the Arab world, Francophone Africa,... and of course Serbian songs about how the Archduke had it coming. Where do you find all that?