Well I got a few books on World War 1, but none in English. If you can speak french/german/italian I recommend you check them out.
>LE NAOUR, J-Y, La Première Guerre mondiale pour les nuls, Éditions First, 2008
French
A very well written (for once) book from the "For Dummies" series. Offers a very detailed insight into France during the first world war. The author is a socialist, but it isn't that annoying. He even denounces some liberal myths, such as the use of colonial troops as cannon fodder, which never happened. Comes with a nice list of books to check out if you want to know more about France in ww1.
>FUNCKEN, F & L, Uniformes et Armes - Guerre 1914-1918, Éditions HIBOU, 1978
French
The go-to reference for any question regarding armament or equipment. Comes with illustrations that literary took 10 years to research. Also comes with a big-ass list of primary references for your enjoyment.
COLIGNON, J-P, Petit Abécédaire de la Grande Guerre, Éditions Le Courrier du Livre, 2014
French
A very well researched dictionary of the slang of the French soldier during world war one. Except lots of puns and dark humor. References a ton of primary sources.
>THIÉROT, J-L, François-Ferdinand d'Autriche, Éditions de Fallois, 2005
French
A biography of Franz Ferdinand of Austria, from his birth, to his assassination. Takes time covering his plans for the United States of Greater Austria.
>MAGENSCHAB, H, Der Grosse Krieg, Verlagsanstalt Tyrolia, 2013
German
A very elaborate book covering the role and actions of Austria-Hungary in the first world war. Supplemented with snips from relevant memoirs.
SIMONIT, G, Storie di uomini dal fronte di San Martino del Carso 1916, Gruppo Speleologico carsico di San Martino del Carso, 2014
Italian
As I don't speak italian very well, all I can tell you is that it's a book about the fighting that took place in the vicinty of San Martino del Carso in 1916, which featured italian and hungarian men.
I can scan any of those, if asked. I also have some good books on ww1 in slovene, ut the chances of finding another slovene here are so minimal I can't be bothered to type them out.