Hi jtisch,
I have wondered this same thing and this has been discussed here before. There are some good web sites. A google search will easily find popular US songs. Also try searching this site.
This web site has Canadian music.
http://www.collectionscanada.ca/gram...m2-3010-e.html
This one includes examples of English and French music--a very interesting site.
http://www.greatwar.nl/
German music of the Great War is very hard to find. I have several very fragile small booklets, about 5x4 inches, with the lyrics only of Soldiers' Songs /Soldatenlieder. I'm unable to translate the words myself but I'd furnish copies to anybody who wished to try. The font is the old Gothic style.
Hope this helps a little!
FliegerJG1