I'm fascinated by colonial soldiers, in particular the sheer ridiculousness of it all. The idea of people on the other side of the world being taken from a their small village or town and being forced to fight for a nation that has a culture entirely alien to their own against another, equally alien nation is fascinating to me. I hope you guys could give me some help in sating my hunger for info on this particular subject.
My dear /u/nowlan101, you've come across a topic which I have been trying to find information about for years. Like you, I am completely fascinated by colonial soldiers (well, maybe not for the same reasons as you since many were not forced at all and some didn't even fight).
When it comes to the soldiers from Indochina then I am going to have to be clear: there is little to no English sources on this subject. There are some brief mentions in more general works of Vietnamese history but are not nearly enough to cover the subject. The only secondary source that actually takes time to tackle the subject on an academic level is Race, Empire and First World War Writing (Chapter 2 - Sacrifices, sex, race: Vietnamese experiences in the First World War) published by Cambridge University Press. There are plenty of French sources on it, but if you're like me and can't read French, then that makes life a little harder.
Here are some suggestions on French sources:
Lettres d'Annamites - Lettres de Guerre, Lettres de Paix by Jean Marquet. A compilation of letters written by a Vietnamese soldier and released shortly after the war.
Les Troupes Coloniales dans la Grande Guerre by Claude Carlier and Guy Pedroncini (ed.) Contains a chapter on the Indochinese participation.
As a bonus, here is some clear archival footage provided by the website for the French Apocalypse documentary on WWI.