The French Soldier has a totally thankless role in All Quiet on the Western Front. He takes cover in the same crater as Paul, and Paul promptly stabs him. (It's war, y'all.)
The soldier then spends the rest of the day and night slowly dying in excruciating pain, his only company being the man who got stabby with him in the first place. The next day he dies, not having spoken a single word.
As far as cinematic deaths go, it could be worse…but not by much.
But despite playing a small part, the French soldier proves important to the film—he becomes Paul's foil (or character that provides a contrast for another character; see "Character Roles" for details).
We know almost nothing about him except that his name is Gerard Duval and he has a wife and child back home. And we only know this much because of Paul's brief glimpse at his paperwork. (Yup, Paul stabs him and then goes through his wallet.)
In contrast, we know volumes about Paul: his family, his history, his friends, his hopes, and his despair. But we see that each man's suffering is equal, and that the sanctity of their lives is equal: Gerard was the one who kicked the bucket, but it could have just as easily been ol' Paul.
And this makes Paul ruminate on the absurdity and randomness of war:
PAUL: You see when you jumped in here you were my enemy and I was afraid of you. But you're just a man like me, and I killed you. […] We only wanted to live, you and I. Why should they send us out to fight each other? If we threw away these rifles and these uniforms, you could be my brother, just like Kat and Albert.
It isn't difficult to infer from this quote that both men have the same nature—and fate—despite fighting on different sides of No Man's Land. Both want to live, both want to return to their families, and both are willing to kill the enemy to see it happen. It just happens that Paul was quicker on the draw than Duval.