will realize that battle's (:= battle is) are but stupid words
for silly games they used to play.

Auch inhaltlich: Schlachten sind keine dummen Worte, sondern verqueres Geschehen. Schlacht ist nichts als ein dummes Wort für diesen Wahnsinn. Und das wäre dann: 'battle is but a stupid word for silly games..', oder eben auch: 'battle's but..'

Und mit: 'to kiss again their mother's cheek and wife's lips and sister's brow' habe ich rythmisch Probleme. Ich würde dann nehmen 'to kiss again their mother's cheek, their wife's soft lips and sister's brow' (was am Ende dann die Stirn sagt, nicht die Augenbrauen [brows]) oder eben für 'wife's' dann women's.

Also sähe es für mich dann so aus (was ich ändern würde, habe ich fett markiert):

Wherefore, my friend, we're fighting here
this bloody battle, tell me, what
we are killing for - dishonour rules wherefore
The enemy - a man like me, began his life like you'd begun
remember, friend, a loving mother's beloved son.
How many killed on battlefields are never to come home
to kiss again their mother's cheeks, their women's lips and sister's brow?
Instead of this they're staining now
the fighting grounds
with purple blood of theirs
and as you listen you may hear
the begging pleading crying
and sometimes, friend,
the silent sound of praying.
My buddy soldier, are you thinking now how this will end for us?
Wherefore, my friend?
Let us accuse this slaughter fury hell
But even more, let's take a stand and pray,
there'll come a day, our children, friends,
will realize that battle's but a stupid word
for silly games they used to play.