/u/nmw is the sub’s expert on World War 1 poetry, but he’s only (as far as I can see) discusses it in the context of English-language literature. However, while waiting for a more direct answer, you may gain some insights from reading his answers sideways and might give people who know other poetic traditions context to respond to.
I think his most concentrated answer on War Poetry is:
He doesn’t address poetry in other languages, but does discuss specific aspects of the British education, art, and life that he credits for the particular development of these famous War Poets.
He also talks in this post about how War Poets have taken a special place in English literature, after only Modernism, and even if there was ample writing in other languages, it might not have the same retrospective place in the Canon that it does in English. In a short section in a longer post about the legacy of G. K. Chesterton (all of which is worth reading), he discusses
When students are taught the English literature of the early twentieth century nowadays, the primary emphasis tends to be upon the Modernists, with a perhaps secondary focus on the War Poets. Authors like Virginia Woolf, Ezra Pound, T.S. Eliot and James Joyce are the "big names" of the period, and many is the student who is exposed to things like Mrs. Dalloway, "In a Station of the Metro", "The Waste Land" and A Portrait of the Artist as a Young Man as exemplary works. There's nothing wrong with this, to be clear; these are all amazing works, and we'd be presenting the period poorly if we left them out.
But there was just so much else going on, and much of it even more popular at the time!
And again here:
Think of what you know of the poetry of the early 20th century. That's when Modernism took the world by storm, right? The big names are T.S. Eliot, and Ezra Pound, and H.D., and so on. And then there's also the war poetry, by the likes of Siegfried Sassoon, or Wilfred Owen, or Isaac Rosenberg -- all held up now as iconic, matchless, vital.
Here, his point is about the retrospective treatment of the literature, not its specific creation or even initial reception.
Again, it’s something for people knowledgeable about poetic traditions to build on in subsequent answers, rather than a direct answer to your question!
Perhaps the most noted war poem in German is Georg Trakl's Grodek. Trakl was a medic in the Austrian army and was (like many) unprepared for the scale of carnage and death made possible by an industrial war. Deeply stressed, there seems to be some question as to whether he killed himself or over-medicated himself and got the same result. The poem was written after the 1914 battle of Grodek, and was the last poem he wrote:
At evening the autumnal forests resound
With deadly weapons, the golden plains
And blue lakes, above them the sun
Rolls more darkly by; night enfolds
The dying warriors, the wild lament
Of their broken mouths.
But in the grassy vale the spilled blood,
Red clouds in which an angry god lives,
Gathers softly, lunar coldness;
All roads lead to black decay.
Beneath the golden boughs of night and stars
The sister’s shadow reels through the silent grove
To greet the ghosts of heroes, their bleeding heads;
And the dark flutes of autumn sound softly in the reeds.
O prouder sorrow! you brazen altars
Today an immense anguish feeds the mind’s hot flame,
The unborn descendants.
You can read it in the original here . It's not simple German. When I was a 2nd year German student it was a really tough nut....unlike, say, Owen, the language is not very transparent. But in some ways the disjointed imagery better carries the bafflement about the new horrors of a new kind of war.